I have 2 570ss and I can tell you they are rock solid TM's. There are a few reasons I went this route versus a CDS direct drive.
1. Heat, the 570 produces a lot more heat than the CDS Salsa unit. The 570's with the temp set to 225, you bill burn your hands on the solution lines. This is also a plus when dual wanding.
2. Dual wanding. The 570 is more than capable of dual wanding up to 600 feet of hose pull. This means that as long as I stick within 600 feet total between both wands I am fine for vacuum.
3. The 570ss has a liquid cooled Kabota Engine. Not an air cooled unit, the means no head gasket issues like stated above with air cooled engines. If the engine is serviced properly, you can expect over 8000 hours of operation. My brother has a Kabota tractor with the same engine, hours on his tractor are over 10,000. These Japanese engines run forever.
4. Less fuel consumption than a direct drive.
5. Less ware and tear on vehicle engine.
6. Worst case scenario van dies. You can move 570 into another van for the cost of a van. The direct drive you will need to purchase a van and purchase the new direct drive parts to put the unit into another van. Direct drive system for the front end can run up to 4k.
The only advantage the direct drive has over a slide in is training tech when you have multitruck buisness. That isn't something I worry about, you put a truck log on the truck and things that got overlooked before get done.
I am really considering 570ss for my next TM purchase. Glad to hear you have liked your machines. How many hours do you have on your machines? How often do you dual wand? I am wanting a system that is truly dual wand capable. Probably will mostly use 250 - 300 ft of hose, one line at like 150ft the other at 100ft. But I want screaming vacuum that is not dependent on what the other tech is doing with the wand, whether it is on the carpet or not.