I can't comment on which ones are BIFL but I looked though my purchase history and can list the ones that I have bought and how long each lasted.

Almost always it's the batteries that fail. One of those Waterpiks on the list I wired in new corldess phone batteries about every 6 months.

I would think a lithium-ion battery toothbrush would probably last longer for that reason. I can't remember but I think the last time I was looking for lii-ion toothbrushes the only thing that was available were those Amazonified clones that come up on the first page when you search for anything on that site.

Oral B ProVantage 1500 - 1yr 8mos and still working fine

Waterpik SR3000 - 2yrs 2 mos

Sonicare 3 series - 2 yrs

Waterpik Sensonic - 5 yrs 6 mos

Waterpik Sensonic - 2 yrs