The other thing to mention is that will it take a SIM card? There have been problems with android and eSIM not working and sounds like it is not just a problem with Visible but other carriers as well.
The IMEI checker is for the new plans. A few that have said don't believe it are still on the old plan including myself. There has been a couple posts where those that have taken the SIM for a new plan and moved it to an old phone and it still works but there have been at least one that can get messages and calls but can't access internet. So if it isn't compatible who knows if it will work.
Last, I like Visible because of the affordable plans bad thing is if you have problems support is really bad and your only options are chat, Facebook Messenger and Twitter. Chat last time I used it a month ago was a 45 minute wait and see some wait a lot longer. Twitter was useless as my questions were never answered after 10 days. FB a couple weeks ago to get some more answers about switching only took 45 minutes for a reply with subsequent responses within a few minutes. There is no customer service phone number to call which is why the plans are so inexpensive.
A shameless plug now, if you decide you want to switch you can get $20 off your first month using my code or link https://www.visible.com/get/?3qJzF8 code is 3qJzF8.