First of all, obviously is the cost. Granted, the money we have invested in our vinyl "justifies" the cost of an ultrasonic cleaner.
The pads of the Spin Clean are gonna get dirty with the cleaning process, as is the fluid. So you need to schedule a cleaning session and get rid of the fluid whereas with ultrasonic, you can clean one record if you wish. Yes, the fluid in the US has suspended dirt in it as well but there is no brush issue.
I had a lot of fun doing Spin Clean on garage records with my daughter in the past. We were a team. I would do the spin thing, she would take the records and dry them with cloths and put them in a dish drainer. When fully dry, we reassembled the records and were good to go!
Now that she's out of the house I like the pushbutton convenience of the Audio Desk.
Also, you can buy laparotomy sponges on Amazon way cheaper than from Spin Clean. And you can wash them: no softener please and you have to cut off the blue tags or they will become hopelessly entangled in the wash!
Good luck!
Paul