Bath Bombs can be expensive, depending on where you buy them. They're usually so big, and that got my thinking; "Is all this necessary?". In short: No. I asked my husband if he wanted to help me (aka do it for me) cut the bomb in half. It took about 5 minutes, and if you wanted to take it further, you could cut it in fourths. As long as the bomb isn't a bubble bomb, you should be ok to do this. I didn't notice a decrease in the effect the bomb had on the bath water. It probably would have been easier to cut along the seal, but the flat bottom made it easier to hold. The excess powder can just be scooped up, and thrown straight into the bath water along with your freshly new half fizzie, or placed into a little baggie to use later.
The bath bomb is from Basin, I can't remember which one it was as we've had it for months.