I've had a few of the ACOG fibre's in stock in the past, they are really neat in regards to not needing any batteries, there's nothing to maintain, just work out of the box. I used a 4x for a while but found it a pain, would rather have a 1x but it's all down to the type of style you play.
Build quality is pretty decent for a clone (well the ones I've had in), some come with trades some don't, made by loads of difference factories all over the place I would guess. £99 is a tad high yes.
Hope that helps a little.