.24 is good, you can make much longer rockets without it wobbling all over the place. I think the game is more solid and stable. I have not tried the new features out. Meckjeb works fine but does not show up in the 64 bit version.
MechJeb is almost essential, even thou people say it is cheating, it adds functions like the Smart A.S.S so you have buttons for prograde, retrograde, NML+/- etc which Orbiter comes even with basic install. Having to manually turn the ship towards the prograde position is a PITB.
The Maneuver Planner part of MechJeb is very impressive, you simply click and select your target, choose the function you want to perform and click create&execute node button. Everything is done for you, I have noticed if you choose hohnmann transfer, if you do not match planes with target first it will fail.
2.2 Change periapsis
2.3 Change apoapsis
2.4 Change both periapsis and apoapsis
2.5 Change inclination
2.6 Match planes with target
2.7 Hohmann transfer to target
2.8 Transfer to another planet
2.9 Fine tune closest approach to target
2.10 Intercept target at chosen time
2.11 Match velocities with target