I have yet to install them, but I really need to.
From my understanding, deans offer much less resistance compared to tamiya connectors. (especially compared to small tamiyas) Since there is less resistance, there is also less heat, so the electricity flows better. (?)
They can supposedly increase your ROF by a few rps (up to about 4) and they increase trigger response. They are also a lot more durable and won't wear out like tamiyas. Apparently they are also much easier to connect. (I'm sure you've had the issue of trying to connect the tamiyas....) lol
I really need to get some for my G36K because there are 2 pairs of small tamiyas on it. (one from the gearbox to the gas block and from the gas block to the batt) Just plugging the battery into my GB alone increased the rps by like 2 lol
I have yet to come across someone who didn't think it was worth the switch. If you are worried about sharing/charging your batteries, just make a tamiya to dean adaptor.