Dave,
That valve is slick, no servo just plug it into your gear channel, last 2 i used no programing needed just plug and play.
It acts as the servo and the valve and linkage one hose in and one out.
With spring airs there is only 1 air line so it cleans up installs alot.
And there about the size of a micro servo to boot.

Those robarts look like they will be the 20-size retract of choice if the price is better then the spring airs.
Spring airs are great but weight and price is the only down side.

-Jason

PS I dont even know why i put retracts on.
I have yet to put them up in flight, i always have in the back of my mind that i tweeked my gear back enough on take off they will get wedged up.
Our field is fine shale with no grass to be found,so one gear up landing is well, bad very bad !
I use them on my starfire but the looks on that plane can only improve.