I like that in-line TDS meter they put with the $199.00 system (you will likely spend at least $35 on a TDS so the pricing is excellent even though over your budget). I bought one last year and it is very convenient. It looks like the one I have and will immediately show you either incoming or outgoing water readings by flipping a switch. I rarely use my hand held one now.
I wonder if their canister DI resin units are any easier to refill than the standard tube type. I never get mine to seal on the first try, no matter how well I clean the gaskets.
The quick connects are highly desireable but I think most units use them. The in-line pressure gauge would be nice to have - won't help my low pressure problems but at least you can see what you are dealing with at the unit.
The backflush seems to help the shut-off really shut off and is supposed to extend the RO filter life.
They don't mention color coded tubing and I recommend it. It is a simple thing but really helps when you assemble and reassemble component parts.
One other comment. You may note that both AM and esquid's recommendations show clear canisters. This is VERY helpful for determining when to change filters on the sediment unit (not much help on the carbon though), especially in my area where we have a lot of fine mud in the water.