The tl;dr is that yes, it works, at least with the smaller shank (8mm) router bits.
But there's a few gotchas.
DeWalt D26204 models and variants
First, to explain, the D26204K, sometimes known as the D26204K-XE, is a 240V plunge and/or fixed base router.
Most routers are strictly one or the other, hence this is a nifty and compelling feature.
This model is sold in Australia, New Zealand, United Kingdom, and other enlightened countries that use 240V.
It's comparable to the North American DW611 model – that's where it can get confusing when talking to people in North America, including our Leigh friends in Canada.
The D26200 is the router with fixed base. You may want this, but the combination pack is better value and more versatile. Note that this model is often recommended on Shapeoko CNC machines, so maybe you might. This featured as part of my selection criteria. But if you're not doing plunge-routing, why are you searching for information about Leigh's dovetail jig, huh?
The D26203 is the optional plunge base – you'll only want this if you bought the router, or the router with the fixed base, previously.
The D26204K is the SKU for the whole kit – router, plunge, and fixed base (and other doodads in the box).
DeWalt D26204 collets
Depending on your or the seller's location, the router will likely come with either a ¼" or 8mm collet.
A ¼ inch is the same as 6.35mm, but it's important to note that you can also get 6mm collets.
You can, theoretically, fit a 6mm shaft router bit into a 6.35 (¼") collet, but you absolutely should never, ever do this. It will fuck up your collet, but more importantly your stomach, when a bullet-sized piece of metal comes flying towards you at around 350km/hour.
This is a bit to one side, as most of the more common / smaller Leigh dovetail router bits have 8mm shafts.
The problem for Australians is that seemingly no one in Australia sells this model router with the 8mm collet.
And, as always, we get shafted (ha) by being a distant island (or perhaps just because we put up with it) for pricing on an after market collet.
JPM Tools in Melbourne sell an 8mm collet. Ask for:
COLLET & NUT 8MM OF97-DW620-DW621K
The guys there are very helpful, but either way you're looking at A$65 for two small bits of metal.
The collet on the router just screws off, with the internal (splined piece) dropping out.
Once you've got an 8mm collet, you're ready to use most of the Leigh router bits.
Routers, collets, reducers, bits
There's a bunch of different router shaft sizes. I used to think there was ¼ and ½ inch only. Sadly, no.
There's metric versions, and not just in a couple of 'standard' sizes. Especially when it comes to twist (drill-shaped profile, good for pulling out lots of material when doing long, repetitive, and/or deep cuts) formats, where the width of the shaft is often the same as the width of the cutting profile. This makes them cheaper to manufacture at the other end -- single piece of material -- but a bit of a bother at the user end. Everything's a trade-off.
Any router has a maximum size collet it can take, and then you can put reducers inside that if you need to. Reducers have a minimum thickness to be effective and safe, so for example you can't have a 6.35mm (¼) collet and get a reducer down to 6mm. You need two different collets.
The D26204 maximum collet is 8mm. As noted above you can get 8mm and 6.35mm (¼) collets, but you can get others too.
From England, via ebay, I found a 6mm collet that fits this router:
Dewalt DE6950 6mm Replacement Router Collet & Nut
This will cost you A$51
Using the D26204 with the Leigh D4R Pro dovetail jig
It works a treat.
I have a couple of other cranky old routers, including a ½" Bosch beasty – a blue one, so you know it's good.
This is the GOF1300 ACE, and it dates back to 1996 – it's known to have a bunch of reliability and accuracy problems. It spent a few years hanging upside down in my Triton router table, and it's never really forgiven me for that. The plunge bit doesn't really stick well anymore, there's some wobble during plunge, it's stiff to move it after it's been up (or down) for a while, that kind of thing. Plus it's heavy as get out. For dovetail work it's good, because the mass grants it some useful inertia, but the baseplate is enormous, and consequently you can't see much of what's going on. Also that inertia gets a little tiring after a while, especially if you're mostly doing softwood that's relatively thin (say 20mm or less).
I also have the Black and Decker KW850E, dating back to 2005. This has a 6.25mm collet, but I couldn't find any alternative collets to fit it. It's lightweight, but a bit black and decker.
The D26204 is lovely - soft start, variable speed, rock solid plunge action, lightweight.
For most of the my work – pine, 20mm, the thinner / standard dovetail bits, happy to work slowly and carefully, etc -- it's effective, safe, comfortable.
The only challenge when using it with the Leigh jig is that because the base is not huge you need to move the unused fingers closer to your work to support it better. It really helps if you've got the exhaust accessory – the snappily named VRS (Vacuum and Router Support). I have found this a bit tricky to set up, and it seems to slip / droop over time, but the extra support is incredibly useful, even on a lighter router like this one.
The dust-sucking capabilities are impressive too. Running a router over end grain for a few lengths while making dovetails without a vacuum option is a great way of covering everything for several metres around with really fine wood splinters. With this thing attached it's a 5 minute clean-up job to get the small amount of waste it missed.