While T-Mobile's internet solution is great for those who don't have any other options, if alternatives are available, I would not use it as a primary means of connecting to the internet, especially for business purposes. As a secondary WAN connection in a multi WAN failover scenario, I think it's more than suitable though.
If you need a static IP, you're not going to get one and you'll be behind CG-NAT. The gateways they provide are combo modem/routers that are of questionable quality and have no bridge mode or passthrough option. So if you want to use your own router or security appliance you will be double NAT'd in addition to being behind CG-NAT. While I would hope their business offerings are bumped up the totem pole a bit, their home internet has a low QCI. Due to the nature of cellular data, your speeds and latency will fluctuate. Unless you are very close to an n41 site, you'll probably bounce between n71 and n41 (if available), especially if your business is in a brick building, or manufacturing plant or other environments were higher frequencies do not penetrate well.
I work about a mile from an n41 site, and I lose about half of my speed from the time I get out of my car to when I get into my office. While mid band is much more resilient to distance and obstacles compared to mmWave, you're not going to see anywhere near the best of n41 indoors.
If your business relies on the internet to function, cost should not be the #1 concern because you get what you pay for.