The swing up threading tool holder that I just did was in steel but I honestly can't tell any real difference in use. My lathe only has about a 350-400 watt motor so I really can't push them that hard. The A2Z CNC QCTP comes with aluminum holders. If I had a big lathe, be a different story. I also made them a bit beefier than the original ones, but that was to use the little 3/16 HSS tools. I can squeeze in a 1/4 bit as well but so far the 3/16 seems to do just fine and I really can't take really heavy cuts anyway.
The AL was my first time cutting dovetails and I was using scrap AL from work ( free- Yay! ) so if they don't hold up in the long run, there really is no loss.
The last update is that I finally bolted on the 4-jaw chuck for the first time and I bored out the last holder for a 1/4in round HSS bit that I am going to grind for boring. I am out of little 8-32 screws anyway so I can't make any more until I get the screws I have on order. I plan to make some more later. It just feels rich to be to the point of making stuff instead of having to buy everything. That gets old really fast.....

They are a lot of fun and I am getting in lots of practice.