I don't have a hybrid RAV, but it would appear that Toyota has designed the hybrid system to keep the battery at the proper state of charge without the need for expensive add-on chargers/maintainers, so buying one of these most likely would be a waste of money.
I only get intermittent use out of the traction battery, almost always it's down to the recharge level when I park it at home, it would be nice to charge the traction battery overnight so it's more useful for the next drive, maybe the 4.5 Hybrid will be a plug-in.
Snake oil at best, dangerous for the battery's health at worst. You NEVER want to charge that battery beyond the system specs.
Also a very good way to completely void your hybrid system warranty. which is 8 years/100,000 miles. The synergy drive system manages the NiMH battery perfectly as it is.
I've only used a battery tender/trickle charger ONE time, about 10 years ago, during the winter while my 85 Vette was being stored in my Mom's garage. The damn thing burned out the power supply to my digital dash. Never again for me.
I do not see anything for 4,4 hybrid as yet. These have generally very good reviews on Prius chat particularly for 2004-2009 ( gen 2) vehicles. I believe these would be good to have down the line as after 7-8 years.