"Is it worth it" is a question that's very tied to your personal values - so it's hard to answer.
The Carbon Doser (well, the original one) is a cheap regulator with a $20 clippard mouse solenoid attached to a $.50 555 timer chip and a variable resistor. The 555 timer just opens and closes the mouse solenoid rapidly. Mouse solenoids are really reliable and have a rated lifetime of like a billion cycles. The rest, who knows?
I'm not a big fan. It's a decent idea - but it should be a $60 product - and failure mode could be basically wide open. I prefer mechanical control to electronic here.
The direction I went with mine is a really good needle valve - basically surplus/used medical devices - that are capable of metering CO2 at low pressures to an insanely fine degree. You know how your cheap needle valve basically goes from no Co2 to OMGCO2! in like a quarter turn? A good precision valve will go 20+ full rotations before its releasing anywhere near as much CO2 as a 1/4 turn on the cheap valve.
I paid $24 for an Aalborg VM3-SV, and $16 for an Aalborg flow meter it would fit in (ebay). Then another $25 or so in various fittings (clippard check valve, some adapter nipples, etc). Currently I'm running only about 10ml/min through my reactor via peristaltic pump, and pH is a slight sinusoidal line from 6.21 to 6.23 (couple hours offset from the tank's ph cycle), with absolutely no electronic control - solenoid open 100% of the time.
Here's a thread on planted tanks - its a list of like a million valves that will work well -and show up on ebay/etc pretty regularly.
www.plantedtank.net
If the link doesn't work - thread is "Precision flow valves selection for our CO2 pressurized system"
