We recently got a cordless SDS and it's just amazing how much time gets saved. No more 100' extension cords taking up space, or the inevitability of asking your customer to run a big extension cord through their lobby because the external outlets never worked... I drank hitachi's kool aid though, already swimming in 18v batteries, and they've seemed to hold up longer.
Here is a fun tip for installing stud mounted letters without the fancy vacuum. More often than not your hole is full of dust, and if you don't get it somewhat clean, all of your silicone balls up with a nice coat of dust. Just bring a baby nose sucker, shove it in the hole, give it a squeeze, profit.