The horizontal speed on higher tier jetpacks is often too much, causing servers to lag when loading chunks, and the inertia/slowdown makes it hard to stop with precision. Throttling down helps this a lot, but the vertical speed, especially in hover mode, is way too slow. An option for throttle to not change vertical speed, but only change horizontal speed, would fix this.

I came here to say the same thing - I much prefer this mod over Simply Jetpacks 2 (more interesting recipes, plus the tier 5 emerald jetpack not descending in hover mode is a godsend) but the one thing that SJ2 does right is not having vertical speed tied to horizontal speed.

To use the emerald jetpack for building you have to turn its throttle way down (which is fine :)) to get that good horizontal control, but that means your ascend/descend speed becomes comically slow. Each time I start a new server I always have to go into the config files and mess around trying to work out which setting is the right one to change to try and get the vertical speed right for low-throttle use (but then obviously it's way too fast at high throttle!)

Edit: I'm doing it now for a new server and just can't seem to get it quite right.