Not too bad. I have used both frozen water bottles and "blue bricks". I'm able to keep temperatures within 1-2 degree range without too much trouble. While lagering it requires checking/swapping bottles 2-3x per day - usually first thing in the morning, when I get home around 5, and right before bed.
My basement is around 60 degrees and I was able to get down to the mid-high 40s. 53 degrees was no problem at all, ever during very active fermentation.