Cheers @beng1968 .
I must admit, I bought 2 more Athena kits sometime after this post was made and can't concur with the opinions here.
The casting was spot on and it was very good value for money. Considering it comes with everything you'd need to bolt it onto your engine, I'd say it's good value.
I will agree it's not YZ rip roaring performance from stock, and considering the extent of tuning on my DTR, it's still nothing compared to a stock Aprilia RS 125.
However, it's not without its merits. The extra CCs give a nice broader range of power, which as I've gotten older I've come to appreciate more (I'm no longer 75kgs wet ).
I did take my cylinder to Mick Abbey for further porting and there is still more porting work that I need to do on my setup. It should be a decent bit of kit, when setup properly.
The first experience I had was when I loaned my brothers 2001 DTR back in 2010, he'd fitted the Athena kit amongst various other mods, and that went very well. At the time, I went all in on a ported 3MB00P cylinder from the TZR Belgarda and that setup definitely served me well. I haven't been on my DTR for several years now and I am eager to fire it up again to rejudge my opinion.