The basic idea makes sense, but more as an oil nutter DIY project, rather than buying this gadget. It could be combined with a revival of the winter-summer oil change idea.
The advantages are:
Packaging: Younger cars than mine don't seem to have ANY spare room under the bonnet, so adding anything is a challenge.
Failsafe: If something goes wrong offline you might have an oil slick if you havn't arranged containment. If something goes wrong with an online bypass you might have a seized engine.
Control: Online you pretty much have to assume operating engine temperatures and pressures. Offline you could change those. For instance, you can get high performance spun propylene filters for drinking water here quite cheaply but they have a maximum temperature of 60C.
When I had metal settling out of my oil, even simple offline sedimentation under gravity might have made a useful difference over six months