The Flip up breech did anyone like them?

[max headroom]

I have not really tried a 57 so don't know if their accuracy is below par when compared to say a 77. If it was not noticeably worse then the alignment issue might not be anything to worry about. All the fixed barrel loading solutions seem to have at least one "con", as below.

Loading tap - sealing requires precision fit and alignment is also dependant on quality engineering.
pop-up - no sealing issues, just alignment concerns
sliding cylinder - could be dangerous plus adds extra weight
RB rotary type - long tp and a bit fiddly.
flip up - long tp
sliding barrel ala Airlogic Genesis - fit of barrel needs to be good or no better than a wobbly break barrel

Have I missed any??

yup. missing.

[Hsing-ee]

That's a point - a gate type system (like the HW 57, Gamo cf-20, or the ASI centre), but using a probe like on the SLR or goldstar to directly seat the pellet from the gate to the barrel...

Short TP (only needs to be a pellet's length), not fiddly, and safe. Just a bit tricky to engineer.

The Hammerli Single and Master CO2 pistols and their match-rifle derivatives were accurate to the point where they would win international competitions. They have very short pop-up breeches, very finely engineered. The Hammerli 4 and 400 series were the only tap-loaders which could achieve 'excellent' accuracy and these had small diameter loading taps, perhaps Hammerli realised that you have to get the tap or loading gate just right for it to work well.

Perhaps it is down to the precision of the engineering rather than the design per se. A sliding breech is still the simplest and most forgiving of the various designs I think, where sloppy tolerances and poor workmanship will have the least impact.

[Solvo]

Modern manufacturing techniques should e ale to remove almost all of the accuracy issues associated with pop-up breech blocks.
For example the Steyr rifles fire directly from the magazine and achieve excellent accuracy.

[Hsing-ee]

Modern manufacturing techniques should e ale to remove almost all of the accuracy issues associated with pop-up breech blocks.
For example the Steyr rifles fire directly from the magazine and achieve excellent accuracy.

Excellent point. The power pulse is different on springers compared to HPA guns and CO2, however, so perhaps that is a factor as well.

[Shed tuner]

The power pulse is different on springers compared to HPA guns and CO2, however, so perhaps that is a factor as well.

very much so...