HVLP spray guns for use with a compressed air system are different and not interchangeable with those made for use with a turbine air source.
Conventional HVLP guns use air supplied in the 25 to 35 psi range and reduce the pressure within the gun such that the pressure at the air cap is HVLP compliant. Turbine guns have large internal passages to allow use of a low pressure turbine and the supplied pressure is not reduced within the gun.
Turbine type guns are available in a range of qualities and prices the same as conventional HVLP guns. Like yourself, I picked up a cheap used Fuji turbine which seems to be in good shape and is a well known brand. It came with a siphon feed no-name gun which is about the equivalent of a bug sprayer. So far, I haven't been inclined to spend $250 or so for a good gravity feed turbine gun just to see how it would work as compared to some decent conventional HVLP guns I already have. IMO, the biggest drawback to the turbine systems is the hose that's about the size of a garden hose, and that is something that isn't gun dependent since it takes a large hose to pass the large quantity of air at low pressure.