I picked up a harbor freight ultrasonic this past spring. It was cheap enough I don't regret the purchase but I don't think its necessary.
Pros - it cleans parts fast. It easily cleans the tight spots that are normally difficult to get to. It cleans brass fast.
Cons - compressed air is absolutely necessary for blowing out water in larger parts with places water can hide - so you MUST completely disassemble all bolts, slides, frames etc. You cant just drop your assembled 1911 in there. It does not polish brass - not like a tumbler anyway.
I don't use mine much, but there are times that it comes in handy. The harbor freight one is a good deal. Its identical to the lyman. and about $40 cheaper.
However, sonic cleaners with not replace your normal cleaning tools, solvents and brass tumblers.