I went to US with their connection which was AT&T. Network coverage was not a problem but as soon as I landed in US the connection was not working. It took around 36 hours for it to get activated. The billing & payment was a problem with these guys. I asked for the itemized bill from the customer service but they never gave it to me. When I came back to India it took them 5 days to take the SIM card back & later they charged me extra money for those 5 days.
The billing system seems to be a bit weak in their office because the after the SIM was returned they said you are going to receive the final bill & the final amount will be deducted from my credit card. But even after that there was some amount due which they charged & never sent me a bill in spite of me sending them continuous reminders.
Apart from billing & payments they seem to be good. But after returning from US I have found out that taking their connection for visiting US is not worth. You can get a new connection(that too much cheaper) from the airport or from any nearby market. Many hotels/motels also sell these connections(all prepaid).
But as of now this is the only company sellingn such connections so customers really do not have any more choice.
Henry