Have anyone here used lens adapters with infinity focus?

I use a Nikon D3100 and have access to some old Pentax Takumar K-mount lenses. I can get an adapter from ebay (see link) with a little minus lens built in to allow infinity focus. What is the quality like? Is it worth buying?

I Know the lens and camera must be used manually, this is no problem.

link: http://www.ebay.co.uk/...0877773154

Added (1). I'm not bothered about metering, My Weston Master can do that, as I say I'm quite happy using manual settings.

I didn't know there was a slight teleconverter effect

Yes I have used an adapter (with glass) to mount a Pentacon 135mm lens onto my Nikon D300 - worked fine.

I haven't seen reviews for that particular model. Here is a Canon FD to EOS adapter.
http://www.bhphotovideo.com/...er_FD.html
Among the customer reviews, many are pleased that it works, but some are not so pleased with the cost in image quality of the corrector lens.

I was always told; Screw/bayonet = no problem.

Bayonet / bayonet = bad idea.

The rare occasions when I need a 50mm, I use my old Praktikar and M42 adapter on my EOS, but I'd never dream of trying it with my various bayonet systems.

It really depends on how fussy you are, these adapters with the optic can degrade the image quality as well as acting as a teleconverter, I for one stay away from any optical adapters because of the huge variation in quality and opinion, however as a Nikon shooter, you have little choice but to either use F-mount or optical adapters.

I would say however that with a D3100 it's doubly not worth the trouble since you lose metering as well with non CPU lenses.