I must have signed up for NSSN a long time ago, but only recently have actually done any shops for them. Their cable/internet shops are super easy if you are a subscriber to that cable/internet company. Basically all you have to do is go in and pay your bill. Pay is $15 for 2 minutes in store plus reporting time, but they are frequently bonused to $25, and you can shop once every 30 days. I've turned off the autopay on my cable bill just to remind me to pick up this shop every month and so it doesn't look weird (you can still make a payment if your payment is already processed, but like I said, it seems weird to me, esp. doing it regularly).
However, I said that they are easy to do if you are a subscriber. I would not want to have to do the non-subscriber scenario, because the narrative could be killer- they want a play by play of your interaction.
Also, they use their own system (not prophet/sassie/etc). The system works fine, but it doesn't send you an email telling you that you have selected a shop or any reminders to do the shop. If you're used to that/count on that, it can trip you up a bit, but usually when I select a shop it's due within a few days, anyway, so it's harder to forget.