Probably the smaller Pirhana would do the engraving just fine. But, you'll need to check with NextWave to make sure the laser will fit and can be used with the 4th Axis. I have no information one way or the other.
The other option is to just peruse their Web-site / store (http://shop.nextwaveautomation.com/shop/
) and find the lasers, and then look at the machines they're recommended for.
The main question you want to ask, however, is this: how far you'll be taking it? Pens are great, but what about miniature souvenir baseball bats? The thing is, the CNC is such a central part of the systems you'll build up (vacuum, maybe a blower, a light. I have a mister and chip blower and a vacuum and a compressor...) that swapping it out for a different CNC later on will disrupt those other systems, making you have to re-do some of them, at least partially. So, (disclaimer: in my opinion) it's best to get the BEST CNC you can get for the budget you have. Spend all you can, get the accessories you'll need, like a good spindle with a good coolant pump, some good clamps. My point there is that some things, like accessories bought from the mfg, in a few years, the company won't be producing those anymore. And with SOME products that have been in-market for a while, that day is coming soon. So, it's entirely likely that if you opt out now, that in 2-3 years, you might not be able to get the kit you want. So, for the base systems, get the best you can afford, and for the accessories, get all the OEM ones you even imagine you're going to need. That makes the OEM happy too
The Pirhana are small and versatile, while the HDs are larger, bench-top machines. They're better, by far, but no machine is perfect. And Sharks, well sharks, rumor has it, have no bones...only cartilage. So, they're not very stiff; they bend easily. Oddly enough, such is the case with these CNC machines as well, since many of the structural components in the stress-chain are made out of HDPE plastic. Say what you will, it's not cast and ground iron. So, if you have the buckage, and you think you want to progress into larger projects, or even metals, think about a larger machine, think about workholding, and think about rigidity. Yes, I'm serious. Rigidity should really be your #1 criteria, even ahead of size and spindle HP. If it's not rigid, you can't get an accurate cut, and if it's REALLY not rigid, you can get cuts that ruin the part and break long bits...often.
Anyway, hope that helps.