I think you are mistaken that they are a PFT outfit. I say that because the way I understand it, PFT companies take your money for you to occupy the seat of a required crewmember. At Key Lime Air, some guys (who don't meet the mins) do pay but they do not occupy required crewmember seats. They sit in the right seat as SIC's. Key Lime's 'Ho's and Metros are all operated under a single-pilot certificate (since they are freight-only, for the most part), so how much actual flying you do etc is all up to the PIC. If you "pass the personality test", he may let you fly all the time.
I worked there for 2.5 years it it is generally a good outfit. By that I mean good MX and decent airplanes. I had a ball flying there, the guys who work there are great guys. I flew the Metro the entire time.
I'd strongly recommend it even if it's a lateral move for you. The experience carries a lot of weight among airline hiring boards. Not everyone can fly single-pilot freight, so if you live through it, it's a definite positive.
Going to work for them will NOT be a bad mark for you, to answer your question. QOL has gone up there since I left, from what I understand. Your goal needs to be PIC turbine time, so ask about time to upgrade to the Metro and weigh that against time to upgrade at a place like Great Lakes.