I also have read that their contracts contain a non-disparagement clause, and that they will threaten to sue and keep the IP rights to the software they develop if you leave them a bad review! So yes, I'm going to go with a different development company.
That's bad. Is a contract like this legal in the US? Sounds like they forced their customer to be happy regardless of the products they developed for them. They do have many portfolios on their website, which is odd since most of them seem to be business-related apps. Maybe most of them don't really care about the quality of their apps anyway and just treat complaints from their customers when they feel like it.