DIY is practice at learning new things and implementing what you've learned. It's a very good thing in that sense. Also, a healthy DIY (or maker, if you prefer) community is good as a check on commercial offerings. If businesses try to overcharge for something or don't offer it on acceptable terms, and you have a great need, having a 2nd way is important.

Making your own HRV may or may not be worthwhile for everyone who does so, but more people learning how to make one is doubtless a good thing.