My favs too, I learned a lot from him when I first bough "Makin' Magic" in the early 90's and subsequently bought more. He was tight with every drummer Pat had (Roy Dyke, Nicko McBrain, Clive Edwards, Tommy Aldridge, Sandy Gennaro etc.) and I especially love his work with Nicko.
He played with the Gentle Giant-ish prog band Gnidrolog in the early seventies and right before he joinen PT he was a member of famous British (free)jazz drummer John Stevens' Away and played on his 1975 album. That album's lineup sans Stevens played on Amalgam's "Another Time" (1976).
I've never heard anyone not liking Mars' playing. He was mainly a P-bass player but sometimes used a Dan Armstrong plexiglass bass (it's heard on Traver's 1977 BBC gig w/ Edwards on drums and Mick Dyche on rhythm gtr) and on the back cover of "Crash 'n' Burn" he is shown with a maple necked Jazz w/pearloid block markers, or at least the neck is from Jazz Bass.