Dirt-cheap extension/macro tubes -- yay or nay?

[epp_b]

I currently have a set of close-up filters. They work pretty well for isolated subjects with distant backgrounds where the distortion is unnoticeable (eg.: flowers, insects on plants, etc.), but the distortion and severely shallow DOF make any of these shots difficult and clear shots of things on straight surfaces impossible.

I can get a really cheap (as in, less than $30) set of extension tubes on eBay without any CPU contacts and only use my 50mm manual lens. Should I spend more and get extension tubes with CPU contacts for metering or spend a bit more yet for a used proper macro lens?

 

[tasman]

I got some from Ebay too. They work ok. I use a manual lens with them, because they dont have the CPU contacts.

 

[epp_b]

And? Are the shots sharp and clear? Do they reduce too much light?