The construction is steel for the spindle with alloy for the cage. They weigh in at 353 grams and are therefore don't weigh a great deal.
A friend of mine has a pair of these on their fixie and swears by them. They are apparently fully serviceable. I am not sure I would be able to do that but as they retail for anything between £14.99 - £24.99 (if you look around) they are are not that expensive to replace. (Although my fixie friend says they are virtually bulletproof).
Also included in the box are reflectors what simply click in to place. To my view they make a rather elegant design look ugly, so I won't be putting them on. Good that they include them of course and nice to know they are there should you change your mind.
Of course they don't fold and there is no fancy quick release mechanism. To be honest I am not sure they need them. They are very light and compact and even unfolded, they don't get in the way a great deal. I have put them on my Original Orange Brompton and so far I like them a great deal. They are much better than the last pedals I was sent and I even like the colour.