From Amazon reviews, I see most people are happy with their handy work. For people whose replacement failed, the seller replaced them promptly and made the buyer happy in the end. I haven't done it. I feel that I wouldn't hesitate if I need to replace it myself.
At T-Mo's web site, one can see the base price for any number of lines in a plan, and, the small print says "Taxes and fees additional". I think the additional amount can be substantial (something like $30 or more). Can you tell us how much your friend's monthly cost is? How much is the "additional" cost? Thanks!