We've had two of the Omnistor 'caravstor' variety (basically the same as the Fiamm 'caravanstor')
Good points:
Fairly quick to put up (we had the 4 metre version and it was definitely a 2 person job)
Rot proof - can be rolled away wet without problems
Stylish - matter of taste, but I like them.
Fiamma version (not Omni) can have additional side/front panels added - very expensive though, and rather defeats the object of a quick canopy.
Disadvantages:
VERY suceptible to wind, and if they get flipped over the van you will know about it!
Must have one leg lowered in heavy rain to prevent the rain puddling in the centre (this is obviously more of a concern with the larger versions - which also get supplied with an extra rafter pole)
Biggest concern - they are not really suitable for use on British caravans. They (as you know) hang from the awning rail, UK vans have the awning rails screwed into the van from the side - so the weight of the canopy is acting to pull those screws out (this effect can be made worse during travel)
Continental vans, otoh, have their awning rails screwed downards into the top of the caravan, hence weight on the rail tends to pull the screws even tighter. Additionally, many Continental vans have a reinforced section along the 'doorside' edge of the roof specifically to mount a a Fiamma/Omni awning (including the 'box' type a-la-motorcaravan style)
Damage to the caravan was a constant spurce of woory to us - and it was a pain to put it away every night 'just in case', particulalry as it aslo meant putting away everything else that couldn't be left unprotected.
We now use a Spacelite, bought specifically because its single pole design means no damage to the caravan if the thing gets blown down.
If an enclosed space is not important to you I would suggest an NR sun canopy - very simple to put up and more wind resistant than the Fiamma/Omni canopies (and, obviously, no chance of damage to the awning rail)