Portable wi-fi

Do you not have a cell phone?

To answer your question with any degree of helpfulness, it would be useful to
know the specific device you are considering (if you are looking to purchase one),
where you will be traveling, what carrier you would consider using/eSim you would
purchase for the device, and what device you would use in Europe that you
would connect to the portable router.

Otherwise, any anecdotal replies are hard to apply to your situation.

Probably wouldn't be an eSIM. More likely to be a physical SIM you'd use in an LTE modem / router type device.

Also, Europe is a big place comprised of many countries. A little specificity on where you're going might help with your question

To shoeflyer' point, I am not even sure you can get it "in Europe" or if you can how open the access will be: https://cepa.org/article/kremlin-throttles-the-internet/ /s

A portable wifi device creates it's own wifi network, which you then access with your phone, laptop etc. The thing is, you may as well just use mobile roaming, rather than buy/rent another device.

The thing is, you may as well just use mobile roaming, rather than buy/rent another device.

It's useful if you've got a laptop and a phone, or a couple of folks with laptops and phones. Especially if you've maybe got some work to do in the evening or something. It's better than tethering a phone.

A few years ago when I was working in events I bought something similar to this for one of my clients. Meant we could get a little network for a few machines outdoors.

https://www.tp-link.com/uk/home-networking/3g-4g-router/tl-mr100/