In reply to dmor9: Both the DMM Brenin and the DMM Alpine (and similar ones from other manufacturers) are poor harnesses for proper rock climbing as opposed to just top-roping.
Centre harness like the DMM Alpine, Petzl Pandion, Black Diamond Vario have a single point belay loop which is great for attaching a rope to, and for abseiling, but the loop is orientated the wrong way for belaying. It makes teaching novices to belay unnecessarily hard and tends to engender bad habits. They also generally only have one gear loop.
The DMM Brenin is much better in that it has a proper belay loop. However it still only has one gear loop which has a tendency to slide around. Also they are a pain to adjust and have nothing to keep the leg loop straps properly centred. They are a decent enough option for teaching someone to belay and top-roping, both indoors or outside, but are very limited beyond that.
I'd suggest a better option might be a Petzl Corax which you can currently buy for the bargain price of £40 from Decathlon. If you are only likely to take male friends climbing then a size 2 (29.5"-41") should be perfect for your needs. If you are likely to take both male and females climbing then, admittedly it is much trickier but even then, a size 1 (23.5"-35") should suffice for much of the time.