This really is an excellent product, but the first time you use it be sure to allow plenty of time, and be prepared for plenty of pain!
Once you've got the initial run over and done with, repeat treatments will of course be pulling far fewer hairs, and I promise will hurt far less too.
I think with hindsight it might have been better to wax first, and then start using this epilator a few days after to catch any missed hairs and then of couse to strip the regrowth. That might have made it much easier.
I've used this in and out of water, and not really noticed much difference to be honest, but the convenience of being able to wash the unit and attachments under water is a definite plus.
If anything, I found it harder to use on wet skin in places (ie under-arms where the skin is not as tight), as it tended to snag the skin more rather than gliding. (I haven't tried using shave/shower gel with it as suggested in the manual, so maybe that would be better.) Fine on wet legs though, but no better/worse than dry to me.
The smartlight is a great addition - even in what I consider reasonably good light, it shows up hairs that I would otherwise have missed.
Overall, I'd highly recommend this, but would suggest lots of short, quick strokes for the first attempt rather than long sweeps, and start with lower legs rather than anywhere more delicate! Keep skin taut while using, move fairly slowly and take your time.
Expect redness too - especially for first use. I looked like I'd been stood knee-deep in red paint for an hour or two after! Having said that, repeat uses have hardly produced any redness at all.
Invest in a good, gentle moisturiser, with as little rubbish in as possible, for using immediately afterwards to soothe (I use Lush's Dream Cream, but a plain unscented cream/lotion with a drop or two of tea tree or lavender oil in would work fine to cool and calm the skin.)