I see your points. But....
1) He likes the sound of the thing. That's a big deal.
2) If he gets a gig-worthy cab now, he can always get a gig-worthy head later.
3) I was BLOWN AWAY when I learned that 30W was PLENTY to gig with (assuming a good cab). I did lots of gigs with an Ashdown LB30 into an Epifani UL410 or a Euphonic Audio VL210. I had volume for days. (These were pretty good gigs with a Nashville baby act, not just Stinky's Bar and Bait Shop.) So, depending on how his journey goes, that little 5W sucker might even get the job done. If he's playing with a mature guitar player and electric drums, the odds are even greater. We haven't even factored in whether an eventual band would go IEM anyway.
4) The journey itself is part of the fun, AND part of the learning process. He'll learn plenty by simply exploring his options. One of the reasons I want him to get into a store and simply "play around" with bass gear is that right now he has very little real-world data to compare to what he knows he likes at the moment. By messing around with several cabs he'll probably come up with as many questions as answers. That's a GOOD thing. Plus, he'll likely fire up a few amps while there. It's possible he could hear something he REALLY likes from a combo or a head. At that point it'll be "Never mind. THIS is what I want". (We've all been there as well. You head down one road thinking you know exactly where it leads. A sudden turn takes you in a completely different, but awesome, direction.
In short, there's no need to sweat the details until @Super_Knack gets to spend some time with some bass toys!
Have fun exploring. Come back and ask more questions as needed.