I have never used one but on paper it would seem the STX is a strong competitor to Proline.
FLI cameras are awesome but they lack any guiding solutions. FLI does not appear to be planning any autoguiding products, development and relies on other manufacturers products.
STX has several including self guide. Self guide is still a viable guiding solution that handles flexures which Proline users tend to have to deal with usually by MMOAG otherwise the sheer weight is a problem unless you are using CDK, AP scopes that are proven to handle that weight.
Autoguiding has not advanced much for a long time and its overdue for some technical improvements. SBIG has done more work here with the various autoguiding techniques - perhaps their worth is to be proven, but at least they are leading the development.
Until you get round stars with 10 minute exposures you haven't even left the station yet on almost any setup (AG12 excepted
).
How to achieve that requires more than just a good mount.
Greg.