Having had the machine on demo for a week I can answer some of your questions but as I have never worked a Scrubba Delux there will be answers I cannot give.
The RV360i does a really good clean, because it is rotating with 3 jets and 3 suction slots per revolution - much more then you can wand.
The speed of rotation can be controlled to suit differing pile types ie low profile commercial all the way through to domestic and their varying lengths.
I found the machine cleaned very well, and left the carpet drier then my wanding - which I was well satisfied with anyway.
Dry passes are easy - you just take your hand of the spray controller handle and do dry passes - as easy as.
I have no idea how ling a head will last - I presume a long time if you dont abuse (like anything really).
There is a felt seal which is important to keep clean - easy to get at to maintain and should only cost a few quid to replace, but you get a spare with the machine.
Reasonably light at 39lbs but with enough weight to do its job.
The Hydramaster RX20 gets good reviews but is about £1k dearer, and is VERY heavy. So much so many c/cleaners dont use it regularly unless on big commercial.
RV360i will be suitable for larger domestics due to its comactness, ease of use and lightness.
There are other heads that can be changed to very quickly so hard floors can be cleaned, or stairs, or a carpet brush with suction for really bad carpets.
Make sure you get a 360i because the 360 had some electrical problems that are solved on the 360i.
Cheapest supplier was Solutions Cornwall and very good after sales support as well. Other suppliers I found were Altec and Ashbys.