1) have a specific price for every single network makes it impossible to calculate which will be the final real cost for each country
2) it's crazy expensive outside the US. Every player in the SMS industry is 4x lower on average. IE: http://www.mailup.com/pricing/sms/
3) they don't support text as a sender. In many countries you can have "MyCompany" as a sender instead of a generic number or short code. This makes the communication much more effective.
4) They claim the pricing will be different for transactional & marketing traffic, but it's not clear how , they just provide one only price list.
5) first 100 messages to US numbers free (each month). I expect they will be soon abused and they will retire this offering.
6) they don't support 2-way communication
7) SMS prices usually go down when volumes increase