I'm curious what others think of frost bomb and how it jives with the frost spec in a PvE setting.
I love the bomb itself, and I really enjoy that it's easy to manage because we never have to keep more than one up at a time, like the others do.
On the other hand, the cast time and frequency of casting frost bomb interferes with my fishing for FoF procs via frosbolt casts. I've found that I get more procs (both FoF and BF) when using living bomb or nether tempest.
Mathematically, the three bombs all produce a similar expected number of Brain Freeze procs. Personally, I enjoy the reliable nature of Frost Bomb's Brain Freeze--it means as long as I have FoF charges and Frost Bomb on the target, I can get ready to pop Alter Time and get all these procs twice in a reliable manner.
As far as FoF proc rate, again, the time differences between the three bombs are not very big. Nether Tempest and Living Bomb take up less and less of your casting time with haste due to how DoTs and haste interact, whereas Frost Bomb specifically scales with haste. This means that the other two bombs will tend to get out of your way more as you get more haste, while Frost Bomb will continue to be cast at the same frequency compared to Frostbolt. This effect is somewhat slight, however, and the haste scaling of Frost Bomb means that, as haste levels rise, you should see more Brain Freeze procs compared to the other two bombs than you did at lower levels.
Really, I'm just not convinced it actually leads to less procs. Now don't get me wrong--there are sure conveniences to having another instant spell instead of a cast time one. I definitely appreciate what that tradeoff is. It also feels like a more frequent burden--because it is--than the other bombs. I think Frost Bomb is at something of a disadvantage for single target in the sense that requiring a cast time does give it less usefulness than the other two. In an AoE context, however, I like not having to switch targets (which NT would demand) or the freedom not to burn a major glyph slot to do the same thing (which LB would strongly benefit from). So for AoE, I feel like Frost Bomb is the more fluid, easy-to-use choice.
Finally, outside of a raiding/boss fight context, I find lining up pet Freeze on freezable mobs to land just before Frost Bomb's explosion to be very in line with my own idea of the mage--something capable of big, powerful hits. Frost Bomb can give that in ways NT and LB never will.
So in a way, I feel like I like the same things about Frost Bomb that you do. As far as the proc rates go, the 3 bombs should be fairly even in terms of FoF and Brain Freeze (with respect to net number of procs over time). It does seem to impose on our mobility and fluidity a little more than the others, though.