Ok, when I first got the type D, I thought it was pretty fast, but sides loosen too fast. I replaced with old yellow core and it still sucks. Gluing did not work. Replaced with C pieces and it felt really great, but still has loosening problems. I tried it and broke several of my PLL records, but during solves, it just lock up and pop like crazy (do to extremely fast loosening).
Then, I lost the cube.
Today, I replaced another Type D's core and screws with that of type A. It feels just like a regular type D, which I do not like. I tried solving it and have difficulty sub-20. Best average was like 26 (DNFed all pops and did not count them in the average). I even tried a store cube with wrong color scheme and got faster times!
Because the type A big washer won't fit, I could only put in the small washer. (so it felt the same as type D, except it no longer loosens on one side.) The disadvantage, however, is that it's really loose even at the tightest tension. I usually almost never pop on my type A or C's, but this cube I pop just about 1/4 of the solves. I even pop OH (it only probably happened twice out of a few thousand on my type A)!
It also locks up quite a bit. As a result, I get sucky times like over 50 seconds. The average was 43.5. (very bad, usually about 38 on much tighter type A). I did get a nice solve of 31, but that was extremely lucky that I did not lock up/pop (solve itself was just a little easy.)
The cube just feels horrible in general. I don't think I'll get low quality cubes from now on. Just reliable A, C, and Rubik's.