I haven't used them myself but I haven't heard any bad reports about Slingwings - the people who use them seem to rate them. Their build quality is excellent and the design seems good. I've got a Gong 7m wing plus and a Takuma 4m wing ride, and have used a friends f-one 5m Swing wing.
IMO the f-one has the best in terms of low end power - probably because its very light and super stiff because the tubes are quite wide. The trade off with this is that you really feel the gusts when using it when powered up. It seems delicate but so far there I haven't seen many (or any!) reports of them falling apart so the build quality must be good.
The Takuma is built to last - loads of kevlar reinforcing, which makes it a bit heavier, but its super stable, really comfortable, and does everythiing it needs to do. I'd say its top end is better then its bottom end - probably because the tubes aren't as wide as the f-one, therefore it won't be as stiff.
The Gong wing plus (i realise at 7m its hard to compare with the other 2) to me seems to be an allrounder - it's bottom AND top end are both good. The tubes are quite wide so it holds it's shape well, it handles really well - it's comfortable and is stable, it's light for it's size. I was worried that it would be too bulky and heavy, but i've been really impressed with it. Yes, you have to concentrate to make sure the wing tip doesn't catch the water, but it really is a superb wing. I'm 85 kg and can get going in 9 knots + (that's with a GoFoil maliko 280). I know there are people who can use much smaller wings, but we have really choppy conditions, the wind isn't very stable, and hey, I'm a beginner, so there's room to improve. What I love about the Gong is that if the wind is super light, I pump the wing up to its recommended max pressure so it holds its shape, but if the wind is strong (I've used it in 15-19 knots - not the most comfortable but at no point did I feel worried) I use less air pressure so the wing can 'fold' slightly in the gusts so it effectively dumps the worst of the gusts - sort of like the flex in the top of a windsurfing sail.
TBH its hard to buy a bad wing, all the big brands are pretty much designed and built well, but some will have slightly different characteristics than others. I find when you ask people why they like their wings so much, most people will rave on about how good their wing is, but they don't have any experience of any other types, they just love their wing because it's theirs! When you spend several hundred notes on a piece of kit you tend to want to like it!!!!!!
Personally if I could start again I would buy an f-one 6m (because of it's light wind performance) and either Gong (the new pulse range), Naish s25 (not the original), Takuma or one of the MANY others for a smaller wing for when the wind picks up. I haven't used the Ozone Wasp, but from reviews I've seen I'd say it's on a par with the f-one.
Here's a really good comparison of the Naish s25 and Ozone Wasp that outlines the main differences:
https://www.youtube.com/watch?v=DutQgDRV4IcOther things for you to consider is your weight - if you're 90kg+ you'll need a bigger wing in the same conditions than if you are -70kg. Its always preferable to use the smallest wing possible, BUT there's nothing worse than being underpowered. I'd imagine the slingshot 4.2 will be fine for 15knots+ - unless maybe you are 90kg+
Best of luck. Whatever route you decide to go with you'll have a blast for sure
