These are two models of the Su25, with different handling caracteristics, as well as different weapons.
The one that is free is the Su25T, the second generation of the Su25, from the late 1990s, dedicated to anti-tank warfare. It has TV guided missiles. It mostly flies like a brick due to all the added weight (it is noticeably more bulky, as it is based on the 2-seats UB variant with the space for the second seat replaced by more fuel and avionics). It is mostly designed to fire laser-guided rockets/bombs, and TV-guided missiles from standoff range against tanks.
The one you can buy either solo or as part of Flamming Cliffs 3 is the "original" Su25A, from the early 1980. It is much more agile, much lighter, but lacks a lot of the modern avionics from the Su25T, and can't shoot laser or TV guided missiles. It is mostly a "old school" ground attack aircraft, designed to deliver bombs, unguided rockets and fire canon in close air support.
Neither have clickable cockpits, in fact, they are very similar apart from the TV screen.
And as for skins, they are not totally interchangeable, since the SU25T has a big "hump" on the back, being based on a two-seats version.
Here you can see the difference between a SU25A and a SU25T.