the guy you spoke to is full of ****
Having spent silly amounts of money and done days on end of research into the ko3s agu conversion, I can safely say is it VERY worth it.
I got my agu totally standard, and had it revo'd after 6 months to 184bhp and 236lbft, the guys said the torque figure was one of the highest they had seen, and that the highest bhp they had ever seen from a ko3 was 193bhp.
At all the dyno days I've been to I've never seen a ko3 make more than 187bhp, and everyone that came in mine said it felt very strong for a stage 1.
I then fitted a ko3S, along with a front mount intercooler, a full milltek turbo back exhaust, and a set of forge hoses (TIP and DV cold side kit)
That was then mapped with custom code phase 2. this isn't a TRUE custom map, but a file written to work on an AGU engine with bolt on mods and a ko3S. it's a fairly good map, but obviously not a TRUE custom map for your car.
Mine mapped made 238bhp and 290lbft, and the difference was incredible. with the ko3S the car was SO much faster than when revo'd on the ko3, it's actually more economical, and when it's working right, it's VERY fast (quicker in a straight line than a remapped S3)
However......
It's not been without it's problems, and it still isn't working properly now!
When first mapped, it had a boost leak (no fault of CC) which storm (the CC agent) fixed for me. When I picked the car up, after 30 minutes, it started making a high pitched squealling noise on boost over 10psi. Storm said this was probably a tiny boost leak, and that I just needed to tighten all the clamps and it would be fine.
After spending around £120 on replacing all the silicon couplers on my FMIC and all the clamps, the noise was still there.
At a RR day 1 week after mapping, the car made just 202bhp and 240lbft, and wasn't running well AT ALL.
I whipped the TIP off to find the turbo was WRECKED, the thrust bearing had totally collapsed, with 4mm of play along the length of the shaft! the high pitched noise was the compressor wheel rubbing the inside of it's housing, not good!
A new turbo later, and a rolling road day to find the car making 225bhp/290lbft, with power peaking at just 4500rpm, at which point the fuelling went dangerously lean.
A trip back to storm, and 4 hours on their rolling road (FOC-very helpful) and they diagnosed a dying fuel pump, with very low fuel pressure causing the big lean out.
Fitted an S3 fuel pump, and it FLEW, it really made a massive difference, and the car was perfect for about a month.
Now, due to running very high boost (22psi) I assume, the spring in my actuator has gone weak, and the pressure within the exhaust housing is no over comming the actuator spring, and forcing the wastegate open, and I'm loosing boost again. I'm going to be fitting a forge adjustable actuator in the new year, and hopefully, that'll be the issue solved.
Every so often now the actuator sticks, and it manages to make it's 22psi boost, and it really is very quick.
Overall, I've had loads of problems, quite possibly due to my mileage (155k when mapped, now 175k) and purchasing a ko3S of unknown history, but I wasn't happy at all that Storm let the car go out with a near ruined turbo, although all credit to them for the day Dave and I spent with our cars on the rolling road to diagnose the fuel pump issues.
Overall I am happy with the mapping and the service I got from CC, it wasn't without fault, but they seemed genuinely interested in solving the problem for me.
All these conversions will have issues along the way, and I've gone for a high power figure with a lot of parts sourced on a budget, so I always expected things to go wrong.
Overall I'd say the conversion is WELL worth it, and you can do it in stages to make things easier.
If I were doing it again, I think I'd fit the FMIC and turbo back exhaust with the ko3 still in place, and get all things like boost leaks and exhaust fitment sorted first. Then I'd just swap out the ko3 for the ko3S and go for mapping.
I'd recommend buying a turbo with known history, my first was from a dodgy guy in east london, who 'thought' it had come from a 75k TT, I paid £180 for it. My replacement was a silenced version from an 04 ibiza cupra, removed at a genuine 26k by a guy I know, and it's been perfect, and was a bargain at just £100!
Sorry for the insanely long post! I just thought it may be of some use to you.
If you're anywhere near plymouth over xmas, or portsmouth in the new year, I'd be happy to take you out in mine so you can decide for yourself if it's worth it.
Nick
