I think you're missing the point Mart. A boat like this is just a start in petrol!
It's never going to be a race winner but it's something that may intice you to 'have a go', if you like it, you may start tweaking and adding bit until the performace comes up a bit. Not many people have the time, money or inclination to source all the "right bits" to make 'a great race boat' and certainly not for £400 in Britain!
So your only option for someone on a limited budget or time or skill is, as Glenn says;
1. A boat like the Flying Fish off ebay,
2. 2nd hand
3. Stay at home and watch telly.
And why wouldn't "that motor in the fish will be lucky to last 12 weeks never mind 12 months", strimmer engines are built to withstand a lot more punishment than in a model boat! Most strimmers are used 3 times a year, thrown in a damp shed, never maintained, run at full throttle on and old petrol & oil that handy and run at full throttle from cold!
Buy one, have a go, you never know we may get some new blood into the hobby!