I've managed to survive without a sonic cleaner. Picks, brushes, compressed air and brake/carb cleaner has always worked for me, but the thought of simply dropping the individual parts into a tub and letting the machine do the work seems like an easy way to free up a lot of wasted time.

I've always had a traditional parts cleaner tank, which is great for scrubbing large items, but the smaller sonic cleaners seem much better suited to the smaller jobs.

This tool won't see heavy use, maybe once or twice a month. What's the consensus on the Harbor Freight model, as opposed to the Hornady or Lyman cleaners?

We have the big Hornady at the shop but have not set it up yet, so no help there. I happen to have a couple of smaller ultrasonic machines at home from my days in the jewelry business. About 2.5 qts. capacity. I have been using them for years on pistol frames, bolts, and other sub-assemblies. It works great at getting into the cracks and crevices. I generally use dish soap, a little ammonia and water. After letting them run for 10-15 minutes I take them out and either air hose them off or heat gun them just long enough to evaporate any liquids remaining. Them give them a good spritz of Ballistol, Safari Charlies, or whatever else is handy. Back in the gun they go after the receiver and whatever else get a good rinse with homemade gunscrubber, ie Hoppes No.9 or whatever sprayed on with a small paint gun. (See Harbor Freight part # 66871, 6.75 oz. paint sprayer) Wipe down as needed, reassemble, and there you have it. I can clean 6-8 guns in very short order this way. Amazon iirc has some Lyman and Hornady product reviews online. One of the smaller ones had a problem with leakage down into the device after a period of some use, don't remember which one though. If you can go the cash, look in the realm of Jewelry grade machines as they are designed for much heavier duty lifetimes. Take a look at the Rio Grande Jewelry catalog for some options.

Sonic does much more than a traditional parts washer, which just gives you a convenient source of solvent and a basin with filter to scrub into.  The ultrasonic gets into areas you'd otherwise need picks and special tools, and does it pretty quickly.

I happen to have a big mondo industrial 7.5gal I can fit entire carbines into (four Uzis with stocks off or folded), or up to two dozen handguns at a time.  In ultrasonic, capacity is convenience.

The larger harbor freights will be better than smaller 2L capacity tanks or even the relatively-nice Hornady "Hot-Tub".  I also have the Hornady, which I use when filling the big one isn't warranted for a smaller cleaning job.  I sometimes do BCGs and HK trigger packs in the 2L tank, when neither the 7.5gal or hot-tub are needed.  I've even got one of those cheap tiny watch/cd sized sonic tanks that go for $15, though I don't use it much since the 2L holds more without being much more trouble to set up or drain or clean.

Having been using an industrial-sized sonic cleaner for 13 months in our shop, I can safely say that it will make short work out of multiple guns and takes a lot of the heartache out of getting crud/residue out of the innards of pistols that I would otherwise have to completely disassemble. At higher temps, I can basically cook old grease and other contaminants out of even ancient and neglected guns. Polymer guns get treated at lower temps, but get just as clean.

The best cleaning solution I have found yet is made by Chem Crest and it's a whopping $85 a gallon, but it goes a long way. I use a pint of Chem Crest to 8 gallons of water, and it gets stuff way cleaner than hand cleaning alone. This stuff doesn't cloud or scum up as fast as Brownell's formula, and doesn't attack bare aluminum like Simple Green, dish detergent mixes or other expedients.

To stretch your formula out longer, do a quick pre-clean on the parts and then blow out the residue with compressed air before putting them in the tank. I get a week to a week and a half out of one round of formula this way, and have less scum to clean out of the bottom of the tank.

Has anyone here tried bagging guns with solvent, then submerging the bag into a sonic cleaner?  Think sous vid cooking guns...  The idea being to reduce the amount of solvent getting contaminated with each cleaning.

So you're talking solvent in the bags and hot water bath in the bulk of the tank? I've done that with small glass jars containing different solvents and small parts, inside the larger water bath - never tried it with bags, specifically.