You might want to poke through the following:
https://groups.yahoo.com/neo/groups/loopantennas/conversations/messagesThis is the subject of a lot of current activity.
I have a 1530, and am very pleased with its overall performance/price. I generally keep mine sited low to the ground (about 6 feet to the top) and this is my antenna of last resort in approaching thunderstorms, but I move it on up from time to time also. I have had this for about 1 1/2 years, and it is generally on 24/7. The only downside I have noted at my QTH is when tuning down at LF; in the high Chicago MW RF environment, a good 500kHz lowpass filter is required to prevent IM junk from showing up on any of my receivers (IQ, R7, R8).
In the past, a concern was that the amp head was integral to the loop, and if the amp fried, you either had to send the entire loop back to the UK for repair, or buy a new loop. New models now have an amp which can be replaced by the user, and this may be an important consideration.