I ordered, by phone, five LED panels 300 x 1200, plus frames from BLT Direct. Unfortunately there was a misunderstanding and the panels that arrived were 6,500K, which was much too blue for me. BLT were really good; they swapped the panels for 4000K ones with no hassle at all.
I surface-mounted the panels using the frames. The frames leave a space behind the panels of 30mm, so the PSUs, which were 25mm thick, fitted nicely.
The minor snag was that ceilings tend to not be perfectly flat, so fitting a 1200 x 300 frame that is perfectly flat can be awkward. If I was doing the job again I'd mount the frames on washers to provide 1mm of allowance for ripples in the plaster board. Otherwise, no problems.
The quality of light from these panels is excellent. I'm really pleased with them.
Bill