There is another thread running re the Milenco levellers and I introduced this item into the conversation. I have been using one for 4 years or so, prior to that I had the Milenco contraption. As others have said, the Milenco can sink if the ground is soft, it does take a bit of winding to raise to any significant height, and takes far longer than it ought to do.
The Lock N Level, in addition to being very easy to use, doesnt sink, doesnt lose pressure over a long stay and the caravan levels very easily once the Alko lock is in place. On hard or sharp stoney pitches, I use a section of old rubber car mat below the bag just to protect it. This probably isnt needed as the bag itself is extremely tough and durable. If I have to use the bag on the offside, I find I am inundated with questions about it and the general consensus of those that have seen it is that is good kit. It is pricey but I feel myself it is well worth the money. It is also far faster to deploy than the Milenco and requires no winding. It is also much smaller to carry than milencos offering.