OMT is something that can be very handy and can help you do the job/task that sometimes no other tool can do or do easily.
HF- basic tool is LOUD, buzzy (hands will go numb in about 5 minute of use), needs three hands to change a blade (one to hold the hex key used to remove the mounting screw, one to hold the tool, and one to hold whatever. It's a pain.), it gets HOT pretty quickly (the tool, not just the blade) and did I mention that it is LOUD? I have one, used it a few times, was/am annoyed with it. It works, both the tool and to do the job/task, but is annoying to me.
The two 'best' names in OMT would be Fein and then Bosch. Their 'recent' (a few years ago by now) change to the yet-another-blade-mounting-system of Starlock actually works well. There are other brand names that make OMTs that are 'good' (various levels of 'good' in there too), but Fein and Bosch are the top tier.
I bought a Bosch (corded, with the Starlock blade system) OMT a few years ago. MUCH nicer to use than the HF. More power, not as buzzy, not as loud, doesn't get HOT in 5 minutes, easy tool-free blade changes. The Bosch felt better in my hand than the comparable Fein and cost a little less.
The one hand tool-free blade release one the Bosch (well two, one to hold the tool and one to move the release lever) is a JOY to use. I didn't like the Fein one-hand blade release as much as the Bosch one. Tool-free one-hand blade release is (should be) a MUST IMNSHO.
Cuts wood, plastic, metal (copper pipe, nails in wood, etc), drywall, grout, etc with the APPROPRIATE blades. Use 'good' brand-name blades, the Bosch blades are usually top-ranked. There are carbide-tipped (tiny little carbide teeth) OMT blades too, just like there are now carbide-tipped recip (aka Sawzall) saw blades and jigsaw blades.
Like someone mentioned, it's a versatile tool that can do multiple tasks. Hence the name Oscillating Multi Tool.
I like the Bosch so much, that I bought a cordless 18V Bosch OMT on sale recently. Bare tool with 'free' battery and charger. Same one-hand tool-free blade change lever as the corded Bosch. No case or storage bag, so I did have to buy something to put it into. It works well for the tasks I've used it for so far.
I've come to appreciate using a 'good' tool more and more. Your call on just where on the price-versus-good scale you want to go. For the 'extra' $50-$100 that the Bosch corded tool was over the next level 'down', I feel that it has been worth it to me. The cordless Bosch was pretty much the same price or LESS than the other cordless 18V OMT.
Controlled flush trimming/cutting of trim or wood floor boards is one of the prime uses of an OMT. That and the flat-blade caulk removal. Or the grit-blade to remove grout. Or controlled plunge cutting to put in an electrical box in existing drywall (neat, fast, I like it better than a jab saw). Under-cut trim (instead of using an undercut saw).. Etc. Multiple uses.
