Earlier, I had posted a blog about the thoughts I put into selecting the right phone & plan for a trip to Tokyo : ipernity.com/blog/stargazer95050/4716358

When traveling to european countries from the US, it becomes easier, as there are very low hardware obstacles. Nearly all modern, UNLOCKED US-phones have sufficient capabilities to connect to the european GSM carriers. There are few (Verizon & Sprint) phones that cannot be used at all, due to CDMA vs GSM incompatibility.
There remains a small possibility of some compatibility issue with some provider's 4G networks. Use FREQUENCYCHECK to see what providers & bands may not work with your phone : frequencycheck.com/compatibility/motorola-moto-g4-td-lte/germany. Avoid providers with 0% LTE compatibility with your phone. If you lack some 4G bands, in most cases it is not a problem in metro areas. It likely only has impact on coverage in remote areas.

New EU regulations eliminated the expensive roaming charges for customers and you can buy a SIM in one country and use it for a limited time in another. With a compatible phone, you can buy a local SIM in a store or order one online and have it shipped to your (US) home address.
WORTH CONSIDERING : Depending on your destination and travel style, you may not need any 4G data at all and public or hotel WIFI may be sufficient.
SOME CAVEATS : typically the period of free roaming is limited. Since you likely will be traveling for 10...30 days, this often may not be an issue. There are plans lasting only 14 days while most last 30 days and a few extend to 90 days.
SOME CAVEATS : often (not always) the SIM while roaming only can make phone calls to its "home" country without incurring extra charges. If you plan to call a cab or your hotel by voice/phone, this could be problematic (not working) or expensive (add roaming charges). You should select a SIM with (local or EU-wide) voice, if that is important.
SOME CAVEATS : not all cards & plans support tethering/hotspot -- in most cases, this is independent of roaming.
SOME CAVEATS : especially seemingly "cheap" cards advertise large 4G data-volume only to bury a disclaimer "3G speeds while roaming" in the fineprint.
IMO this contradicts the EU regulation but if you purchase such a card from the US, it may not apply and you are stuck with that slow speed.
SOME CAVEATS : Local SIMs may actually be cheaper than the (foreign/roaming) SIMs offered online. Ordering ahead of time adds convenience and you don't have to spend time navigating a foreign town to find a store or buying one at the overpriced stores at the airport.
SOME CAVEATS : Some plans & carrier include a SIM in their price. Other carrier offer plans -- and require separate purchase of a SIM. Watch out for expensive shipping charges.
SOME CAVEATS : When roaming, you do not know which network provider is covering you and that can affect coverage & network speed. In remote areas, this can be an important factor (incl compatibility). For my trip to Iceland, I specifically picked a local SIMINN card for that reason.

For my trip to Japan, I decided to have 4G data plan for my phone and ordered it online. OTOH during recent visits to the EU, I chose to buy locally :
ICELAND : I wanted the better coverage provided by SIMINN. 5GB (plus voice) cost ~$25, 10GB (no voice) also cost ~$25 : www.siminn.is/en/prepaid That is not a bad deal and SIM was included !!
PORTUGAL : Using WIFI was sufficient, until I had to call landlords to meet & exchange keys to vacation rentals. 5GB cost 20EUR (~22USD) includes voice-line, SIM and taxes & fees : vodafone.pt/en/products-services/visiting-portugal.html
GERMANY : There too it is not so expensive (compared to US) to get a prepaid card but I think this is DATA-only : 10GB cost 20EUR (~22USD) : www.vodafone.de/freikarten/callya-digital/?icmp=mobilfunk:callya-digital
"Amazon EU roaming" : the cheapest data-only card (with 4G hotspot) sells 6GB of data for $22USD. The cheapest data+voice cost $25USB and has 5GB of data for 4G LTE hotspot. Claims calls to anywhere in the EU, not limited to "home" country.
By comparison a US service : fi.google.com/about/plans cost a minimum of $30USD (plus taxes & fees -- they can add 10%...20% on top of that, may charge extra one-time cost for SIM). For that money, you get a measly 1GB of data. NO TYPO -- it states $10 per GB !!
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Attempting to save money on a data-plan for short travel -- IS IT WORTH IT ?
That question, of course, is very personal but considering the overall cost of a trip, it may be not worth the time to bother about saving approx $20.
You might be able to get a "roaming" SIM for $20...$30USD -- OTOH, if you walk into a local store and pick a SIM with 1...5GB for 30 days, you might get an equally good or better deal and pay $20..50EUR. Possible voice & SMS included.
SAVE TIME : if you urgently need to make reservations or contact a pickup from the airport after your plane touches down ==> buying a local SIM is not for you.
SAVE TIME : by buying a SIM online and have it shipped to your home address before the trip starts. Possibly activate SIM from abroad and have it ready as you land.
SAVE TIME : In Portugal, I was glad the clerk help with the setup of the SIM in store and got it to work quickly. It took me a while to manually get the japanese SIM to work. That was NOT a language issue, as screenshots all showed english characters -- just a steeper learning curve.
SAVE MONEY : Sometimes (not always) the cards sold online for $30 can provide similar service as a local 50EUR ($55USD) card. It also can be that you paid $55USD(50EUR) and you could have gotten same service locally for 25..30EUR.


CONCLUSION :
Looking back, I think the most decisive issue to choose local versus online (US) purchase comes down to the amount of TIME SAVED and the URGENCY to connect again to internet (and voice).
You also may want to add LANGUAGE BARRIER as another reason to favor (US) online order over the local shop. Especially in Japan, I would have had a harder time to find a store selling SIM-card while in US & EU, I can read signs and recognize the various brand names.


Happy trails -- and don't spend too much time online and instead enjoy your stay abroad. On vacation, 1GB of data is a lot -- no need for the 60GB plan.


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