I am new. I only have a poorly developed opinion on balance.
Jump Jet seems bad as a stand-alone faction, relying on Pyro as a robust general-purpose raider that falls off mid and late-game. Most of its units seem niche, overly so, to the point where they are not practical even as a faction to dabble in.
Most notable these are: The Puppy, The Moderator, and The Placeholder
-The Puppy-
This unit seems to want to be effective at reclaiming wreckackage and attacking single large units with overwhelming burst.
In practice its range seems too slow, and its speed and health insufficient to do its job. Its value seems entirely limited to its 'build power', which is unfortunately restricted in only building one bad unit - the puppy.
I would like to see its range increased and its damage lowered to normalize it, maybe with a bit more health as well. If this proves too effective, decreasing its accuracy seems to be a better solution than decreasing its range. As it stands it has been shown to be too difficult to get into range and too unrewarding once it has. This all has the side-effect of giving JJ low-weight anti-air as well, even if it is had.
As a comparison, look at how much it costs in relation to the damage it does now, even under optimal circumstances. It is very rarely cost effective, even if you assume it consuming wreckage. You could instead be reclaiming that wreckage with a constructor and getting something good.
-The Moderator-
As it stands now, the unit seems reliant on an unintuitive and practically exploitative relationship between slow damage and shields. With the existence of the Freak and the Placeholder, this is more lackluster than ever.
Jump Jet would rather like a more functional skirmisher. Well-micro'd pyros and firewalkers serve as effective riot units, but the need for situational long range is real. Personally, I would increase the weight of moderator, and increase the maximum ability of the slow to around 75% - a proper crippling number. I feel JJ is the heavy-weight bot faction and this should be embraced, and I feel their unique positional mechanics should be renforced, but it is important to actually have this unit able to cripple something. If this is realistic, knockback might be useful (so few things have it), disarm, or murder.
-The Placeholder-
I want to like this thing. I really do. As it stands, it is too unreliable, too clumsy, and too expensive for its effect. If it were to remain as it is, I would recommend a slight range boost.
Instead, I would like to see the effect creating a physical barrier across the ground, creating a zone that simply stuck units in their current location, or creating a status effect that prevents movement. Gravity wells are cool, but they are just too unpredictable without some measure of additional consistency (longer duration, longer range, higher arch, etc).
Anyway, this is my view on the factory. I am interested to hear the opinions of others.