The battery "purists" will hate this answer..........
ANY fully automatic maintainer is better than none.
And disconnecting/removing the battery probably does nothing productive.
In order to break even with buying a $100 charger over the lifetime of a 7 year battery, it would need to roughly double the lifespan......compared to the charger you already have.
Not likely that it will make anywhere near that much difference.
If it gets you an extra two years, it won't pay for itself until your 4th replacement battery......or 28 years roughly.
P.S. How many seasons has your present battery gone down to 12.3 and been left sitting that way ??