My own experience with them has been slightly worse than most as I got my Mer IIID conversion through a shop here in Japan. The land of No Returns on model kits. On first inspection, every thing seemed ok. So I spent the $150 USD on the conversion. But when I got it and Tried to mount it to the Merk III hull from academy the peices didn't fit!!!!! So next came a search of the internet and pics that matched were of a Merk IID. To check this I went the closet and grabed my Merk II and sure enough it fit the Merk II lower hull.
To make this worse, I thought it would be a good thing to call the Manufacturer about the problem(I don't speak enough Japanese to make a sensisble arguement about the problem) But after an hour on the phone (international rates apply) argueing with him he finally agree that he mislabled the box and that I could send it back for a replacement kit at no extra charge. Here I thought I was home free..
This was about a year ago. No replacement kit. My Merk III is still a prototype version, My Merk II is still a nice Detailed normal Merk II. As for the Replacment kit It still has to arrive. I think it gone and lost forever, along with the $150 and the Merk IID kit that I sent back to get replaced for the IIID kit.
Since this haas Happend not only has the Japanese shop stop carring and special ordering AEF Designs stuff but they Importer here in Japan has stop working with them all together. I wonder If anyone else does a Merk IIID conversion!!!!! STUG