I guess the main thing is how the efficiency compares to plastic panels. I can't even tell what the collector surface is made of (aluminum? I have never seen panels of this design). The seller doesn't seem to know much except that they are "quality brand" and in good condition. I am trying to get as much info as I can before I make the drive up to see them.
They don't appear to have glass which would change the efficiency characteristics so they should not be too different than standard panels. But it isn't very clear how they are fed. Do the panels have a header? If so, what size?
I ended up buying them. They should be perfect for my application (assuming they don't leak).
The collector surface is totally flat, imagine a bunch of square tubes next to each other except its all one piece. the backside has fiberglass sheeting for insulation which is good because these will be propped up on a flat roof. they will also be much easier to mount than standard plastic panels. I have 8 4x10 for a 13,000 gallon pool