So far it’s been more than enough for what I am doing (wood and leather engravings). I tried anodized aluminum but I can’t say that my issues were too little power – I don’t think I had it focused well enough bc Jay from Jtech has demonstrated the capability with the 2.8W.
I have not tried glass but a mirror is on my to do list. There is another thread around here all about the laser and people’s experience.
The 3.8W would allow you to cut things faster, but I would think the engraving speed would be the same. I don’t think our machine is setup to do very high speed engravings due to the size and inertia of the middle assembly. This is just one opinion so think about what you want to do and see if it is worth it.