The Dual Pro wasn’t available when I bought mine either (August 2021). I decided on the 7W spindle mount. I struggled with the different wattages too, and in the end I decided I wanted the “fastest” one available. I have no regrets on that decision. As JTech points out, the 4.2W will go 2X as fast as the 2.8W and the 7W will go 4X as fast as the 2.8W. The high-resolution lens for an extra $20 was a no-brainer for me, as it creates a higher-resolution spot.
As for the spindle mount, I recommend it because it gives you flexibility AND a good option for fume extraction. I use it when my project isn’t very tall (because there isn’t a lot of clearance under it). I also bought a magnetic mount accessory for times when I need more clearance under the laser (for example, etching a logo on the bottom of a bowl).
As for fume extraction, unless you’re outside, you’ll need it. Engraving wood throws off smoke like a campfire. I found a vacuum hose fitting that slides into my Sweepy dust shoe, and ground the edge off the fitting so it gets up close to the laser. The duct tape is there to restrict the air intake to where I need it.
So for me, fume extraction is easiest when I have the laser spindle-mounted. I have a Stinger vacuum with a charcoal filter that does a great job. If it’s nice out, I’ll open the garage door instead and just blow the smoke out with a big fan.
Here are the details on the fume extractor:
I cut it up, removed the cheapo Stinger filter, and zip-tied the carbon filter material in place. It removes 99% of the smoke, but not the smell of burning wood. Note the smoke residue on the normally-black carbon filter.
The big “X” on my wasteboard happened when I first tried to etch a clear whiskey bottle without a suitable mask on the glass to absorb the energy. Glass is transparent to a diode laser so it etched the wasteboard and not the glass. LOL.