Not speaking from experience but also have been trying to dig up the same info for the past year or so, in search of 15m or 18m to round out an otherwise diverse quiver. I’m searching used (keeping costs down, rare light conditions kite) probably like you, and a learned a couple things you’re going to hear from the experts eventually here:
- V2 and V3 were obviously great kites when they were latest version. Bridle is adjustable but more fragile than hyperlink/soul etc so some will need replacement depending on former use
- fabric improvements - newer kites will soak/hold less water
- I was about to jump for a V3 15m until a post and subsequently various accounts about a known leading edge collapse in some scenarios on the V3 that has been corrected/improved on the v3
- v4 requires concertina folding (but then I was told that previous versions benefit from this also) which to me I might struggle to do on my local beach because its not broad and occasionally littered with driftwood etc
Hope that helps start you off. I may wait for the used v4 market to ramp up. Staying tuned for the experts to correct me if I’m wrong (and contact me about selling a used V4 15m domestically in the US)