Celestron Radial Guider - opinions please

[Jammy]

http://www.celestron.com/astronomy/celestron-radial-guider.html

I've been offered one of these second hand and wondered of anyone has one, or knows if it's compatible with my setup?

I have a Celestron C9.25, Celestron f6.3 focal reducer, Celestron SCT T-adapter with T-ring,  and Canon EOS 600D DSLR camera.

I'm new to imaging, and wondered what other peoples opinions are before I agree to buy it.

I've read a few posts on here that say the distance between the DSLR sensor and the focal reducer is critical, and should be 55mm (I might have this totally wrong).

Is it really that critical? and does this  OAG setup work with my scope?  I know that they're all made by Celestrion, but I don't know if that alone makes everything compatible.

Thanks for your opinions, and help

[Jammy]

I'm also looking at getting a QHY5L-II mono guide camera.  I can then also use this camera with the SCT for planetary imaging.

Not sure if that makes any difference which OAG to use, but thought I'd throw that bit of info in