HTH John, por favor amigo, such a study, if accurate is COSTLY. An an inaccurate or incomplete study would be deceptive.
One of the "biggies" of AGM owner fanaticism is the non need of "watering".
Mounting in locations that have no proper venting.
A greater charge amperage acceptability.
Higher CCA than eqvt size flooded lead acid batteries
IMHO the biggest disadvantage is not price but rather under HEAVY use, meaning continuous full cycle operation, you need an Ouija board or an excellent amp hour meter and patience to determine if and when the AGM needs conditioning. The longer you wait the more unrecoverable hard sulfation may form. Using guesswork a full 30% of the available amp hour capacity may be forever lost. But light duty users who never use their AGM's to capacity will stamp their feet and pout that "That Ain't Possible! Use my eight year old AGM's for example!"
No battery design is perfect for all uses and users. Weigh the PROFESSIONAL pros and cons from RESPONSIBLE companies like Lifeline and Deka and minimize the arm tugging and "pssts" you read on forums like this one - if those posts try to convince you a particular battery "Is The Only Way To Go'.