My course (May 99) did our first jump from the Skyvan then the other 7 from C-130s. I seem to remember the load being 2 PJIs and 2 sticks of 5 or 6 troops. I also remember the green skid marks on the underside of the top half of the split ramp from collisions with para helmets due to over-exuberent exits. The beast itself I remember as a like being in a plywood Transit van with wings.
The advantages were much cheaper operating costs and being able to remount from WOTG rather than trucking back and for to Brize for each lift.
I subsequently jumped from the Skyvan on exercise a few times (including Norway) when C-130s were not available or not justifiable. For a time, IIRC, the Skyvan went out of use and the whole of the basic military course was done from the C-130, but then they got busy again and the Skyvan reappeared.
I was trained on LLP in 1999. I think it had been in use for just a year or 2 before that. Certainly, the bloke I replaced (who arrived 2 years or so before me) had trained on PX Mk4 and had then converted to LLP.