DIY is a gamble, Bill Fitz provides very good measurements for his designs, but countless factors involved in DIY are beyond his control or ability to guarantee success. Then there are other things that need to be considered such as intended usage, volume requirements, a "sound" you are looking for, etc.
I agree that speakers you build yourself tend to sound better, until you A/B them against superior systems.
I have built Bill's designs, Mr. Danleys design, and my own with very good success. I can also state then I have built the DR250, one of Bill's folded horn designs similar to Mr. Perry's DR290, compared it against several MI grade boxes, and it has fared quite well, not just my opinion, but also of other sound professionals present and listening. So my success story with these is for $200 worth of parts and my leisure time invested, I built a box that beats anything MI grade offering. At a recent rave, these little boxes had the best sound in the house. Three rooms, three different systems, one with JBL SRX dual 15 tops, the other with Yorkville fully horn loaded tops. It was easy to walk from one room to the next and listen. The Fitzmaurice horns had the best sound by far. This tells me that for this particular usage, in this particular room, I had the system that fit best. If the rooms were swapped, or if it was a live event it might have been different.
I do not agree with Bruce Gavin, that MR. Perry was bad mouthing the designs, I feel Mr. Perry's frustration in that it is a considerable investment in time to build these things, especially the first go around, and his expectations were high. I think if he built them correctly, he should end up with a very usable box. The midbass performance of these horns is impressive, and since he found his to be lacking, something might need to be fixed.
I find PSW to be an invaluable resource, there aren't many sites on the web with such dedicated professionals so eager to give up their trade secrets to help others up and coming. Where would Evan K. be without the guidance from industry professionals here