Hi Martin. I have one of these
http://www.astroanarchy.com.au/teles...er_80x400.html
On a dovetail on top of my 8” f/4 Newt mounted on a HEQ5 Pro and it handles it perfectly. At 400mm with 80mm apature, it is incredibly easy to find good guide stars. $99 is an absolute bargain, so much so I’ve bought 2. One for my Newt and the other for my SCTs so I don’t have to swap them over when changing scopes. They are a rack and pinion focuser which I find easy to use and easy to adjust without disturbing the guidescope. They have a pretty decent dew shield built in to the front which rarely fogs up too. Personally I feel it’s a great option for guiding.