The HD springs are nominaly the same free length as stock disco springs and just stiffer spring rate. Not so good for maximum traction on rough terrain, but better on side slopes and much better on the road.
I haven't seen the specs for the other bearmach lift springs, but I expect they are longer and about the same spring rate compared to standard springs.
I find HD springs are fine for recreational off road driving being a better compromise if a vehicle spends a lot of its time on road.