Online Recording Studios - anybody here had used them?

Came across a Sound on Sound article recently about online recording studios (like StudioPros or The Missing Track) where you hire session players to provide and play real instruments of your demo tracks for a fee. I always struggle making my bass tracks sound “live” and real so this could be a good option for me to infuse that "live bass’ feel on my songs. Anybody has any experience with these type of service?