Two reasons really.
One is that buying new cams and with solid lifters I can run profiles with different profile that is a little more aggressive... you have to make the choice when you get the cams if you are going to do it.

Even if you dont get these mechanical cams... I have been told that if you drive your car hard at track days with normal lifters they can start rattling even after one day.. (see threads on here). You lose a little power but more that pain in butt factor.

I know you have to fiddle a bit to adjust solids, but I wont be driving that much on road and don't mind fiddling...

Trouble is the aftermarket cosworth ones are sooooo expensive... and these other ones that work fine (so I am told) are a fraction of the price.. Being in Australia its very hard for me to find a parts book for the car quoted... they dont sell them here.
I hope someone can help me with this.

Regards
Gavan