I recently got myself an add-on tele lens for my iPhone. Not this model, but similar. I haven't taken it on vacation yet, but have taken some photos at home and I am pretty satisfied. It is a bit difficult to attach but I hope it will be easier with practice.
I think it is a good compromise between an iPhone and a p&s camera with a zoom - not a replacement for a DSLR.
I'm looking forward to taking it to Madeira in September.