tldr: Beautiful product, makes me and people smile, but quality a bit hit&miss.
I own two halfbike 2s. Both are fun to ride, and we have probably become the talk of a few towns in our parts by now, as many people remark and ask about this amazing bike-scooter-thing.
One of them is 4 years old, single-speed, never had the slightest issue.
This one is almost exclusively ridden by me, 90kg man.
The other was bought this April, and it seems to have been put together a bit shoddily. From the get-go, the brakes were way too tight (i.e. scraping), which could be fixed. But this also showed that the back axle appears uneven, as is apparent in the paint taken off the axle by the scraping brakes (image taken after about 4 weeks!). Additionally, there is an intermittent scraping noise I haven't pinned down yet, as if a tire was touching something. Cadence makes me suspect something front-wheel-related, worst case in the gear box.
This one is almost exlusively ridden by my considerably lighter wife.
So, it's a fun ride either way, and if it's well built then it lasts. But the build quality on the latter one makes me a bit wary. I suspect it to fall apart at some point, probably irreperably.