We have used it a couple of times for STL. Be sure to check the websites for the hotels you are looking at. The last time, I cancelled our PSF reservation because it was cheaper online at Marriott.com.
We’ve used it to just park our car, it was cheaper than the airport. The hotel had a shuttle but we ended up taking Uber, it was still cheaper to park there even with that added in.
My wife and I used it in MKE in Oct. We had a 6am flight so had to be at the airport at 4:30. No problems whatsoever. Picked us up and took us right to our car in the gated, secured lot when we got back.