The ease with T Mobile is there too. I pay $50/month for my plan, and calls, text, and data effectively works seamlessly in ~160 countries. If I want faster data in some of those countries, I can pay $10 extra.

Google Fi is $20/month for voice and text, plus a variable $10/month per GB up to 6GB where it caps out at $80/month.

Note that I'm not arguing against you, just wanted to clarify that the t mobile experience is just as seamless as Fi, in case I overcomplicated it.

T-Mobile even supports WiFi calling in the same way as Fi, if you want to enable it (handy for me at work, where I'm in a building built like a bunker that gets close to no reception on any network).

Also note TMobile supports Apple Watch LTE while Fi doesn’t and probably won’t.

Is 6GB seriously the best Google has to offer? I'm on a 7GB monthly plan and I find that limiting...

I guess we have different standards here in Europe.

As Larrysalibra said, 6GB is basically just the threshold for where you go from paying per GB to it being unlimited. If you use 3GB, you'll be charged $30 for saga. If you use 6GB, you'll be charged $60 for data, and if you use 9GB or 18GB or 30 GB you'll still only be charged $60 for data.

It doesn't stop at 6 gb, they stop charging you for data at 6 gb. It's "free" after that.

$10 buys you unlimited LTE in like half europe.

If you can actually get these plans using Apple SIM - it’d be order of magnitude cheaper.

I've used Travel SIMs in the past simply because although they're more expensive, at least they work and I know I'll probably have coverage.

Trying to figure out how to get a prepaid plan with a good amount of data that'll work everywhere in Europe isn't easy. Then there's issues about recharging the plan, and many of them don't accept foreign CCs, so you need to be in the country you purchased it in to buy a voucher from the carrier's store.

I also hadn't found any 'unlimited' data options on a prepaid SIM - they only appear to be on the more expensive contract plans. At least, based on my searches in France, Netherlands, Denmark and Norway.

Finland has unlimited (without the quotation marks) data on prepaid SIMs from all carriers. Usually for about 1€ per day or 20€ per month. Depending on the plan it will also include unlimited texts and talk.

I ended up using a reseller in Australia to get an "EE" SIM for an upcoming trip - feeling like I've been ripped off here as I paid significantly more than $10

Most of the prepaid SIMs I saw had heavy restrictions on tethering - can you point me in the right direction?

Are you travelling to the UK? There are loads of SIM cards for sale in arrivals, including EE.