I have a hypothesis about DX and tracksaws:
They pretty much all have very good dust collection, as long as they are cutting across a flat sheet of material. But use one to trim or bevel an edge, so that the underside of the cut is hanging off the edge of the bench or whatever, and a lot of sawdust is thrown out underneath or to the side, and not caught by the hood arrangement over the blade.
Given that they usually have two big holes in the hood: one for blade change, to spanner the bolt, and a quadrant where the arbour moves to plunge the blade, there is scope for some to catch sawdust better than others. The Mafell notably doesn't have a hole for a blade spanner (or Allen key), and owners say its DX is very good indeed, so there is variation, but I am pretty confident that most of that variation comes down to the task in hand, rather than the saw design.
@Weirdbeard, don't underestimate how adaptable these things are in use. One big plus is the very easy to use depth setting: I keep offcut strips of 2mm thick MDF sheet to use as protectors under the saw cut. They take up no space, and last for a surprising time, as the blade only needs to make very shallow scuffs for a clean cut (the tearout on both sides is actually better if it only penetrates to the minimum necessary). You also don't need a billiard-table-flat surface for cutting. Within reason the track is flexible enough to cut on a saggy floor, and I have even used the router table to cut on top of (with the MDF).
I get your enthusiasm for cordless - I have just bought a Bosch 10.8V cordless jigsaw - but unless you go big and expensive (e.g. Makita's 36V saw which uses a pair of 18V batteries), lack of grunt will seriously limit the usefulness of a tracksaw, as a battery powered one will be slower, and/or limited by depth of cut and quality of finish or material it can handle.
The finish quality thing is subjective, and I am risking a heated argument, but there is the kerf to consider: both Makita and Festool, and, IIRC, Mafell too, settled on 2.2mm kerf blades at around 160mm diameter. 160mm means these saws will cut almost all kitchen worktops, which must have been a design requirement. 2.2mm kerf allows for a relatively thick saw plate (the main part of the sawblade), which in turn makes it fairly rigid and with lower vibration.
So the cut is cleaner (and the saw probably a bit quieter too), and that is really important as a user benefit (it's all marketing in the end!). But pushing a "fat" blade takes more power than a thinner one. You can use less power by having a smaller diameter or a thinner kerf. Some of the battery saws do use a thinner-kerf blade, and I think it's simply because otherwise battery life would be unacceptably short. The trade-off will be finish quality, but I realise this is very subjective, and contentious. You would have to do a lot of carefully managed side-by-side testing to find out definitively.
Some makers have decided to use identical blades to the mains saws (Festool and Makita at least). Given that a narrower blade would make a big difference to the energy use model (making the design a lot easier), this is, to my mind, quite revealing.
Also, before I forget to mention it, Festool saws (and probably other good brands) should be set up with a tiny amount of toe-in on the blade - the back of the blade is further away from the rail than the front by the thickness of one 80g piece of paper. It's a one-time adjustment, but it also makes a big difference to the cut quality, specifically because it stops the back of the blade scuffing as the saw progresses. So add that thought into the mix, and that it would be harder to achieve with a smaller blade.
So there is quite a bit more to getting that excellent cut quality than just running any old saw on rails or against a fence. If you go for a good brand, I'd expect a lot of life from it and excellent quality. I mentioned I use a Kreg pocket hole kit: it is briliant to just join sheet goods straight from the track saw and get spot-on square joints. I know you can do this on a table saw, but the track saw (and a 'pegboard' table) make the whole business so much easier, for me, anyway.
E.
