I assume you're talking about the Shady Brook Farm marinated turkey tenderloins? I buy them all the time - in fact, nearly always have a package in the freezer. I only cooked them whole once &, like you, wasn't terribly impressed. It's not that they were bad, just sort of "eh". However, I do find them both reasonably priced (we get at least a couple of meals for 2 out of one package) & very handy to have on hand. You can definitely plop them into whatever additional marinade pleases you - I do it all the time.
What I use them for most is kabobs. I cut them into chunks & skewer them with veggies; then either broil or grill them. Delicious. They're also good marinated in a yogurt/tandoori type marinade & kabobbed as well. Another thing I use them for is cut into smaller bite-size pieces & used in Asian stir-fries as a change from the usual chicken.