I have that stamp set too, and I haven't had any issues with it when I used it. It didn't feel any different than other photopolymer stamps, though the design on the stamps was a little more delicate- that could be why it felt thinner?
I've used pigment ink for the solid cloud, rectangle and square (Avery Elle pigment inks), as I tend to do that with solid stamps in general. Regardless of the brand, I always get mixed results with solid stamps unless I use pigment ink. So, it's just become a habit.
For the other stamps in the set, I've mainly used Versafine Onyx black and Ranger's Archival inks. I've found that the archival inks give me the crispest results with sentiments (aside from Versafine) and they have a large color variety, too. That would be my recommendation to try. The Archival ink is especially good on thin sentiments, because they don't spread out as much when they absorb into the paper as dye inks do. The dye inks become fuzzier when they absorb into the paper, which is not ideal with thin sentiments.
Lastly, I have gotten a couple of stamps from Simon that have had issues. There was one stamp set that was in a card kit that was missing a stamp. And another that had a manufacturing defect that basically drew a line through the sentiment. When I contacted Simon's customer service, they sent me replacements for both and they were really great about it. I'm not sure if they'll be able to send you a replacement for the Talk Bubbles stamp (since it's retired), but they might have some extra tips to help you out.
I have been happy with the quality on the rest of the Simon stamps, though. I've got quite a collection, and have had no issues with them.
Simon Says Stamp Quality
