Thanksnot to start an argument but I’ve picked up two second hand beer engines and they are superb. Both needed a bit of tlc but they are so simple and parts are readily available if needed. I have set up per @peebee excellent advice and the beer runs out way before any loss in quality. Both are quarter pint pulls and I just ditch the first pull on each session.
Actually, if you go to the trouble you can seal off the hand-pump's nozzle between pours. You might still lose a few millilitres (beer left in the nozzle) but beer in the cylinder stays sound for days. I very rarely rinse out my pumps once a keg has been attached.