Visible is still current although it's not intended for a router. That doesn't mean it won't work. Some people put Visible in routers and seem to get away with it. You need to activate it on a phone first.
For a more traditional "unlimited" plan, as far as I know, your options are basically Calyx, FMCA or any number of resellers of varying reputation.
I think there are several models of the Max Transit. If yours does band 71 then you might want to consider Calyx or FMCA which are both Sprint roaming to T-Mobile which makes it good for band 71. To use Calyx you need to be prepared to thumb your nose at the terms and conditions and take a risk where it says not to move it to a different device. Like Visible, people seem to get away with it without much trouble but you never know if or when that could change.
For resellers, about all anyone here can do is report their experience. For what it's worth, I was using
this company for a while and they were okay. About a month ago with about three days notice they alerted me that the plan was being cancelled but they had a new plan, slightly more expensive and would send me a new SIM. I told them not to bother because I'm not using it enough right now and I have some other tethering options. My dealings with them were mostly okay and they have a physical store as a local computer service shop which made me feel a little better than most resellers online who are often pretty much anonymous.
I think pretty much all resellers, no matter how good they seem, are doing a little dance to stay one step ahead of their plans being shut down by the carriers because everything I read online suggests that there really are no unlimited plans. Whatever they're selling is probably not totally legitimate for the this sort of use. I think some resellers are better at doing that dance than others.
Other people here can no doubt report good or bad experiences with resellers.