I got the same plan when I bought my Nexus 4. It's been pretty great so far, my only problem being that the entire plan will shut down if you go over your 100 minute allotment (so be careful).
It won't shut down, it will just bill you at a rate of 10 cents for each additional minute used. I usually keep some extra money in my T-Mobile balance so this has never been an issue on the rare occasions I go over 100 minutes.
I've looked for the terms of the plan, but have never been able to find them. I read $0.10/min overage, but what are the details on that? I almost never use 100 minutes, but I'd like not to be crippled when I do.
I think the solution is to keep a bit of extra money in your account, so that they can bill you $0.10/min after you go over. I haven't gone over 100 minutes yet (Skype) so I don't know what happens, but I keep $30 floating in my account.