I too use a rigid guide setup, with an old Meade/Toya 50mm refractor. Solidly locked in with Borg 60mm tube rings (with custom made inserts to bridge the gap). NIL flexure detectable, and it pays dividends in the images as a result. The whole guidescope setup weighs in just a LITTLE over 300 grams, which brings my entire imaging rig to 8.7kg, which is well under the 10kg limit of my Vixen mount (when I finally get to use it in GOTO on Friday - that's what UPS says anyway).
I have an f/9.2 system, reduced down to f/6.4. I see NIL difference in imaging at either focal length, so the guide setup is reliable and good. I went from slightly eggy stars with the Orion SSAG with miniguider, to ROUND stars with the Lodestar and my own guide setup. I found the Orion mini guider system sufficient, but not exact. The optics of the mini finder really let the whole thing sown - I found any stars to guide from HAD to be more or less within the inner 2/3's of the screen capture, otherwise guiding was pretty terrible, thanks to the distortions happening in the finder's average at best achromatic lens system (I too use an achromat, but it is actually rather flat field, and Japanese optics)
James, I have a mono Lodestar (not the newer colour - don't see much sense in that, unless you make it a planetary camera) - no model number or such. I got it second hand recently from Allan Gould on here at a very good price. I have had it guiding (just trials using the Vixen GPD2 setup) some pretty faint stuff - never looked what mag they were - but the Lodestar has been shown to guide at as low as mag 18!!!! (
http://www.sxccd.com/lodestar-autoguider - look at the picture at bottom of Eris!!!!!)