I haven't used TooSIM, but when you use an eSIM for cellular data, data roaming must be turned ON.
For me the key thing to be aware of is the situation with texts. Occasionally a traveler wants to (or needs to) be able to receive a text. One reason might be to respond to authentication texts about online purchases. In order to receive texts sent to your regular phone number, your original SIM needs to be turned on. In my experience, that doesn't interfere with setting the new eSIM as the priority SIM.
How texting works can vary with the type of phone you have (Android/iPhone) and even the manufacturer of the phone. (Samsung, in particular, modifies the Android software in ways that alter some settings.) There is information online about how to manage texting settings when you have an active SIM and an active eSIM, with the latter being the priority SIM. From what I've read, the process is easier if you do not have a Samsung phone.
There are quite a few earlier threads about eSIMs to be found here via the Search function. Here are at least some of them from the last year:
https://search.ricksteves.com/?button=&date_range=1y&filter=Travel+Forum&query=eSIM
