Regarding the QM Achille....
I have had a QM Achille from new (6 years).
I have had zero experience with a Londinium.
*came with double springs installed.
*takes 25 minutes to reach group warmup from cold.
*'suffers' from TS stall.
*makes great shots.
*is very noisy when the pump engages to refill the boiler. (I use mine on the tank.)
I have fitted Gabor's fabulous pressure-profiling gauge kit to my machine. (Thanks, Gabor!
When I did this, I removed the inner spring. Its shots now peak around 8.5bar.
The TS stall is observable with a stick-on thermo strip...you need one of these. After a shot you just pull the lever to flush grounds from the screen...this brings the group up to temperature again. No drama involved with the stall at all.
All of the bodywork is heavy grade stainless steel. With the rotary pump for ballast, it weighs a ton!
I can't see myself ever moving this one on.
Let me know if you have any questions.