so having bought Steve's Outwell Backroads and also a Campervanbits Comfortz Awning Room a few weeks prior (all be it the Standard one rather than the XL version) i can probably offer some insights into my own question here
caveat, I've only used both once
First off weight, the Comfortz one is a much heavier weight fabric despite having less surface area, the Outwell is very similar to their Hillcrest/Fallcrest products if anyone has those... this has both advantages and disadvantages, the heavier fabric is much darker (almost blackout really) and has a more robust feeling, less flappier i.e. quieter in the wind... but i found it much much harder to hang on my own (i.e. doing the zips up and sliding the strip thing), i also noticed with the slight slope on the awning bars, it seemed over time to slip away from the van more than the Outwell.
Space wise there's no contest here, the Outwell Backroads with the slopping sides gives lots more usable space, clearly the Comfortz XL one would negate that somewhat. The Outwell also has doors (& Windows) in all three sides, that can be raised with optional poles to create canopies, or just rolled up, so offers far more flexibility. I also like that Outwell have included an extra velco strip to allow you to move the right wall all the way over if you fancied moving the awning roof bar above the drivers door over, this would give you even more space inside.
Technically you could hang the Comfortz room and not peg it down on a still day, the design on the Backroads means pegging out is mandatory otherwise it wouldn't really work.. again i guess the same would apply to the Comfortz XL, I'd be interested to see how the extra weight on the XL handles the pegging (assuming its the same fabric as the standard)... my Comfort Standard was second had and one of the eyes has pulled out, which i suspect might be due to pegging with too much tension.
Pricewise its a win for the Outwell, its way cheaper than the Comfortz XL one, comparable to the Standard.
Other musings are that i like the Comfortz attaches to the vertical legs on the awning, but then i like that the Outwell can store in the rear chairs as it comes in two bags.
So anyway lots of for and against for each, hopefully that will help some folks too... i think based on my limited experience i will probably lean towards the Outwell as my ongoing choice, my primary requirement was to have something quick and easy to put up when I'm not using my larger awning and know i'm not gonna move the van.
vs 
