I own both... the P8 has been a decent reliable bike, but of course, nowhere near the Brompton in terms of folding/folded practicality - so for me, it's pretty much a car-trunk/lock-up-outside bicycle. It rides nicely, and the larger ballon tires have better floatation on gravel/dirt, but the 2 extra quick releases for the steering stem/handlebar introduces a lot more slop into the system which makes it feel less solid and cheap - although that doesn't significantly affect performance.
The Brompton is more comfortable for me to ride longer distances (suspension offsetting ballon tires or large diameter wheels) and it's my become my favorite touring bike due to its versatility - rigging an aero drop position in my M bars was also a big tipping point, next time I'll go with the P bars. I also have a good gravel bike and MTB, but am interested in downsizing my life and will only keep the Brompton.
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