I got my whole co2 setup for free. I will be upfront, it am about 99% sure it was purchased for growing weed and was left by a friend's roommate who bounced out on him. Now, mine has worked pretty decently over the years but I feel I have the same issues as some of the lower end CO2 systems.
Even though I could maintain a reliable bubble count, the only way I really know how to gauge consistency, it was impossible to make fine adjustments as my "needle valve" or more so, flow meter, was not made for fine tuning.
Even though I got mine for free and may or may not be comparable to lower end regulators (It actually seems to be better), by the time I replaced the important components, I would have paid the same or more than building a great regulator, assuming I actually paid for mine to begin with. That's a big reason I would recommend just building one.
Furthermore, even though I am happy with my reg to a point, I still plan to just go ahead and build another. Partly from curiosity to see if I will get better results, partly for cosmetic reasons, partly because it just interests me to DIY one.
Again, my regulator may or may not compare to other cheap ones, I don't really know.