Questions for the Nighthawk M1 4G LTE Mobile Router

Question 1:

Does this need to have a data-only Plan SIM for the service to work? Rather it be Verizon, AT&T, T-Mbile, etc.

Question 2:

Also, I'm trying to figure out what service would be best for me. Currently I use Cricket (owned by AT&T). Usually in my home, I get 2-3 bars and sometimes 4 bars. Testing with just the LTE for cricket in my home area on speedtest, I get around: 5 - 9 Mbps download, 0.40 - 2 Mbps upload.

Where I'm at work, it is a totally different thing. I haven't tested the download and upload speeds, but especially in my work building, I usually get 1 bar. 2 bars on a good day but at times it does just say no signal, so I'd have to use the Wifi. If I'm not on Wifi sometimes, things just won't load fast or at all, especially addresses on GPS which I need for my job.

So if what I said above is any indication, I feel like I should try T-Mobile or Verizon for this. But I don't know for sure.