When we looked into Roam mobility we felt it was just a reseller of T-Mobile, and we were better off if deciding to go that route, particularly from a binge on perspective was our consideration to go with T-Mobile direct, which we've personally found doesn't have anywhere near as good coverage during travels as Verizon. Bell Mobility put us on T-Mobile for our travel add on roaming package in Florida last year for the first time instead of usually been Verizon, it was a nightmare with hardly ever getting any coverage even in major populated areas on the gulf coast side.
For Mexico we would go with a pay as you go Mexican carrier down there FWIW. TravelswithKevinandRuth (Canadian full timers), go down there a lot and that's what I believe they do always.
For the USA, with Bell now deciding to use T-Mobile for the travel add on, we bought a MIFI (on sale at $21) with a pay as you go with Verizon which works really well for the most part many other Canadian snowbirds have told us. Not the cheapest but it's reflective in a much better coverage area than most others.
