I've known some time about the various levels at which a mana troop can be useful (or not!) at actually speeding up specials. I've seen the guides. They're all written in a way that I find difficult to read, I wanted a more visual form. Especially as I'm finally about to purchase the 19th class bonus for my five star cleric -- How valuable is that 2%, on top of a troop?

https://imgur.com/RFz2ZUH

Not at all! For me. I've got a level 23 mana troop, but the next one is down at 13. I'd have to get it up to 17 before it would help. Laying the data out this way really helps me see and understand better than the guides I've seen to date.

This chart has every level mana troop in the rows, mana speeds in the columns, with 2% and 4% columns for each, for the class emblem bonuses. The cells highlighted in green are the ones where the combined boost is enough to drop the charge rate by a whole tile: e.g. for Very Slow, normally 13.5 tiles, any mana troop at all is enough to drop it to 13 -- from 14 since you can't match half a tile.

https://docs.google.com/spreadsheets/d/17Z_3FTZwVFmn7W6wZvrZlrLU-q9ZOb7Vkq58HPO4vt4/view

And here's the online format. Chart above in the default tab, the other tabs are more interactive calculators that I built on the way -- make a copy if you want to edit them yourself. But I think the chart does its job nicely: You can immediately see that an Average speed hero needs 10 tiles until mana troop level 23, but either a 2 or 4 percent class boost can drop that to level 17.

Hope you find that helpful!