Magnetic cellphone lens attachments are admittedly ridiculous, but given that the HTC Evo has an 8MP camera (albeit sorta crappy), I can understand the draw. I mean, just look at what a macro Evo can do for some Fig Newtons:
Normal. Close-up. Macro lens.
Good and Evo doesn't have a link to the particular magnetic macro lens they tested here, but they're probably right in suggesting that quality won't differ much generic manufacturer to generic manufacturer. Lenses cost about $30. [Ebay and Amazon via Good and Evo via Engadget]