If I can afford the commercial branded equipment from reputable manufacturers in Germany, the USA or Japan, I WILL buy them. These are the benchmarks of well-researched and well-designed equipment. I'd rather drive a BMW than a Hyundai.
I have DIY stuff eg. lightings, skimmer, Calcium Reactor etc, because I need to supersize my equipment due to my SPS corals. These corals really demand a LOT from me and I'm happy that my equipment has not disappointed me thus far. If I had to buy commercial versions, it would have cost me 5x the price. Eeks.
Most DIY projects are based on commercial designs and may work as well as the real stuff as long as one understands the concepts of how and why they work and is able to adapt using local parts to duplicate the working principle.
It takes a lot of time and expenses eg. transportation etc in the sourcing of individual parts, trials and errors with the risk of costly mistakes, compromisation of effectiveness with design flaws and workmanship... sometimes rendering DIY projects more expensive & time wasting than just buying commercial products straight off.
I see DIY stuff as an alternative to commercial products which used to be sold at every expensive prices in the past but thankfully prices has come down locally, even as shipping freight and the strong Euro turn people off from ordering from overseas.
Like I said, get the real thing if you can afford it as it is often better designed and made of better quality stuff.