Using a PH smart controler with common sense is imho knowing what it does and whats going on in your tank when it does. And actualy it only does one thing more then a drop checker does with a timer on the solenoid. Even working only with that without a smart controler can go as disastrously wrong. It's never the devices failing it's the users failing.
Your drop checker also is a PH meter showing a even less acurate color instead of a number. You still need to check your PH in a more acurate manner next to it. As you also need to do regularly with your KH. These thing can fluctuate and adjustment is needed. So with or without controler yu are always checking and double checking.
Many co2 user run on the edge, they asume to have more healty plants if they are on the higest point (in numbers) of the optimal conditions. But that just a falsity, because there is nothing more healthy. It's the same as being dead or alive there is non in between. You are healthy or you are not. There are many poeple running low tech and they have mighty healthy plants as well, maybe not growing so fast but healthy never the less.
If you run your co2 on the high end lets call it Lime Green then you will have not much tolerance, a few bubbles more per minute and you go yellow and could gass the tank. If you'r not at home and the temp rises your co2 presure will rise and you might go over to top come home and see suffering fish. That's the risk of using co2 on the high end of the numbers. And you're not using it with sense you are constantly in the danger zone hand down to the will of mother nature outside your tank.
If the temp drops the bubble count goes down. So regarding to that if the temp isn't stable your co2 is never always as stable as you thought you set it. That's just plain physics you never get around.
Now what does the smart controler do? We don't have to go in to that to deep we all know that already. The downside isn't in the controler it is in the way you think you should use it.
many people use it to rocket their co2 level to the edge in the fasted time possible. It will shut the co2 down anyway if the set ph level is reached. So why would you worry about the bubble count? Make it 40 a minute and you're in less than an hour at top level. And thhat's the dangerous mistake to make.
If for what ever reasen the controler fails, a fals reading or a mechanical malfunction and keeps pumping your realy nuke it all sky high in shortest time possible.
So living lime green on the edge is like driving a sportscar with 100 m/h, 2 feet away from the edge of a deep clif, 1 little bump in the road and you go down the abys. no error margin!
Now if you use it with sense you go just green, your plants still will be healty the only differents is the grow a bit slower. If poeple start to yell we have plants that need the high levels, that's also a falsity.
Because then they only want to makee the impossible possible to let a swamp plant that usualy in nature only grows emersed growing submersed on the botom of a lake. If the plant needs that it simply not a realy suitable aquatic plant. That's the only truth about it. And if you stay just green you got an error margin.
Now back to the smart controler, how to set it? First take a drop checker and hang it in your tank. Put the probe of the controler in the PH 7 cal. solution. and set you bubble count regarding wath the drop checker tells you, make it lime green
and keep it there for a whole day. Now your bouble count is set to lime green drop checker. measure your PH and set the controler a few points lower. Let it regulate the co2 and keep lowering the set button til the DC is just green. You still have to check you KH and recheck your PH and calibrate the controller. These thing you got to do anyway, also with a non controlling pen meter and a drop checker. So telling a PH controller is crap again is a falsity based on nothing. And if you set a controller in a safe way you have something realy nice that will keep your Co2 more stable than without a controler and that certainly never will get you algae. And if it ever fails you're unlikely to go yellow because the previous set bubble count focused on th edrop checker will never reach yellow. At least not that fast or temps must be rising out of proportion.
Stay just green, stay on the optimum of the average and your always safe. Do you still want to grow actual terrestrial plants on the bottom of your lake you got to go on the edge to nuke 'm with co2.
Don't blame the material for your own ignorance.. Thumbs up..
Still my opinion is all that doesn't make a controler worth the price they cost.. it's a rip off..