Harbor freight maintainers seem to have a bit of a reputation for that sort of thing. Some of them are right where they should be for charging and float voltages, others of the same model are under or over voltage. The overvoltage ones will tend to boil off electrolyte. I just don't trust them.
All of the NOCO and BAtteryMINDER brand chargers/maintainers have a desulfation feature. They are also temperature compensated (adjust charging voltages to optimize for ambient temperature.)
Which charger/maintainer and whether to use the standard or the AGM setting depend on which brand AGM battery you have. I checked the recommended bulk charging and float voltages on my Optima battery. It matched up more closely with the standard flooded lead acid battery charging profiles on my BatteryMINDer chargers. A quick note to Optima tech support confirmed to use the standard profile. A odd ball brand AGM in my log forwarding trailer also uses the standard lead acid profile. The deep cycle "VMax" brand AGM battery in my dump trailer and the little Yuasa battery in my UTV both use the AGM profile on my chargers.
I use a BatteryMINDer Model 128CEC1 (predecessor to their current 128CEC2) on its highest (8 amp) setting on the dump trailer, since the deep cycle battery likes to be recharged at a higher rate. This charger also gets rotated around to other vehicles on occasion, since it has a variety of charging profiles and will also charge at a user selectable 2, 4, or 8 amp. It also has better testing and diagnostic indicators than the NOCO chargers and the smaller (1.5 amp) BatteryMINDer chargers. It's expensive, but the flexibility was worth it to me.
I have several BatteryMINDER model 1500 ($55) and model 1215C ($82) chargers. These are std lead acid profile chargers, both 1.5 amp. I believe they are electrically identical, but the 1215C is more weatherproof. I use them on flooded led acid and on AGM batteries which use the same charging profile. I use one of the 1215C on my tractors Optima AGM battery since it is more weather proof. That battery is over 9 years old. (Previous flooded lead acid batteries lasted about 2 years and caused some corrosion problems.)
I uses a NOCO Genius2 on my wife's motorcycle. Low amperage, but has multiple chsrging profiles. (reasonably priced 2 amp charger. can be found for $40- $50)
In the smaller chargers, the small BatteryMINDers have only one advantage over the the NOCO Genius1 and Genius2 charger: The desulfation in the BatteryMINDer chargers are continuous (NOCO only desulfates during charging cycle, note in maintenance mode). The NOCO Genius 1&2 have multiple charging profiles (flooded led-acid, AGM, Lithium), while the small BatteryMINDers are 1 charging profile (works very well on flooded lead acid and some AGM, works "OK" on specialty AGM)
A BatteryMINDER 2012AGM on the UTV (2 AMP AGM profile only charger, but with the diagnostic capabilities of their larger chargers, current price $109. I've had this for years. It has worked well, but since I've got the dignostic stuff on my larger BatteryMinder chargers, I might go with a NOCO Genius1 or Genius2 if I were buying today, since they are much less expensive and will also do AGM profiles.)
A two-bank NOCO GENPRO 10X2 charger (basically two 10 amp, 12v chargers in one housing) is permanently mounted in my 24V antique military pickup. will do standard, AGM, or Lithium. Nice charger, and highly waterproof (rated to IP68) so can be installed where it is exposed to the elements. Unless you need to charge two batteries independently in the same vehicle, a single bank charger would be more appropriate.
I hope some of this answers some of your questions. All of the ones I have listed above have proven very reliable. I have NEVER had one fry a battery. You really can't go wrong with either brand. It's just a matter of determining the appropriate charging profile for your battery and the best charging amperage.
