If the XLT is used, buy it and then sell it when you can get an Edge. If not then wait it out. There are too many targets that need the full FOV of a long focal length scope.
Wise advice here. I really liked the C9.25XLT that I used to own.
Will I have satisfactory imaging performance (APS-C OSC camera and full frame mono with filter wheel) with the non-Edge and a corrector?
I have owned both and in my opinion, the standard XLT version performs well for imaging up to APS-C sized sensors. There's a bit of fiddling needed with back focus to zero it in for the XLT with the 0.63x reducer.
The EDGE works extremely well with both APS-C & full frame. The celestron standard camera T-adapter does an excellent job dialing in back focus BUT make sure you get the model with 48mm threads to reduce vignetting. It works with any camera that's already set to a 55mm backfocus. Both ZWO & (now) QHY have adapters available for their cameras which greatly simplify configuring the camera to a 55mm backfocus.
I've found for both my QHY128C and QHY268M cameras, installing supplied adapters (one being a blade series camera adapter from Cyclop optics) for 55mm backfocus hits the sweat spot for the EDGE 0.7x focal reducer. I have not imaged with the C9 EDGE at f/10 and likely never will given the pixel scale I'm already sampling at.
What's even better, is that I now have three OTA's configured for 55mm backfocus and two cameras with a backfocus of 55m. So I can move either camera to anyone OTA and the field will be flat.
Hope this is helpful.