Hyd or Mechanical Roller?

After reading on a couple of threads here. Have realized there is a Mech Roller lifter, for the LA eng, that requires no modification.

I had about decided that this was going to be my route.............

Went on the Comp Cam sight. It states that the Mech Roller is not good for sustained idle or low rpm ????? Why?

and There Hyd roller for the LA eng requires block grinding..............

Is there a Hyd version out there that is a "drop in" lifter like Brian's Mechanical roller Design?