Chrono is higher performance kite than Speed. Drawback is it is not nearly as user friendly as a Speed, Chrono overflys and collapses easily if kiter is not alert. Chrono goes higher and faster upwind and has amazing hangtime, but 18m size is not a high jumper for normal kiter. If you are not a heavy kiter 18m size is big, I would say too big for a foiling. But I would guess you are a big guy, so 18m may be the right size for light winds.
I wouldn't pay for Chrono v1 any more than for a Speed4, and not much more than Speed3 in good condition. Prices go down surprizingly fast because real target group for those kites (racers) want newest models (R1v2 etc.) and get rid of old kites. I would say for non-racers lesser performance with better user friendliness is a better choice.
Chrono V1 uses the kevlar bridles and is high performance race orientated. It is not as easy to fly as chrono V2. V2 is more like a higher aspect higher performance speed 4. Its a lot easier to fly than the V1. I suspect Speed 5 and Chrono 2 would be very similar but i haven't seen or flown speed 5 yet.
Personally I don't like the V1 18m chrono. Its too big, too slow tends to collapse easy and doesnt improve my low end much from the 12m V1 chrono I have.
I love my 12m V1 chrono though. Its fast, dynamic boosts too the moon and if i'm desparate i can get going 9-10 knots on my door 12m chrono combo.
It is harder to fly than the speed or V2 Chrono. But in my opinion, has more fire breathing dragon in it. So more fun.