I'm a fan of Lil'Gun, using it in .357 magnum, .44 magnum, and .454 Casull.
Yes, it will erode the top strap and forcing cones eventually, but so does every other powder when used at maximum SAAMI pressure levels.
My first .44 magnum was a Ruger SBH I bought in 1971. Over the years I owned it, I fired over 20K maximum loads utilizing mostly H-110, but with a little 2400 and IMR 4227 thrown in. It began cutting the top strap at around 3000 rounds and eventually that cut became about .020" deep.....and then stopped getting any worse. The same thing happened to my S&W model 28.
It's the nature of the beast with the magnums if you use heavy loads.
I've found Lil'Gun DOES produce higher velocities at lower (apparent) pressures than other slow burning ball powders like H-110/WW296/AA#9/WC820. As to barrel heat, the only time I've really noticed it was when using it in a recent range chronographing session of some Lyman 358156 160 gr. cast boolits. This load produced 1550 fps. average, and during the test 12 rounds were fired in about 1 minute. Though the barrel was warm, it wasn't too warm to hold.