Noticed these in my local Netto and was in 2 minds whether or not get one, but with just a couple left on the shelf decided 19.99 was probably not a bad price. It says; 17.5Ah, 900 Amps peak / 400 Amps boost starting power.
Not sure how that equates with the more expensive units out there but it does say that it's not suitable for cars with electronic ignition, or is that just a general disclaimer to cover the manufacturers ass? I don't envisage using the booster very often but with winter just around the corner you never know, and the built in compressor for tyres will be very handy.