Transavia
 

My partner, also PE, has just flown KLM back from SIN upgraded with miles. As part of this the AMS to MAN sector was also upgraded and the usual voucher given. However an economy boarding pass was issued on this sector as the flight was being operated by a cramped one class Transavia plane. In effect downgraded. Apparantly this has been common on this route this summer. Is it worth a letter?

Probably not. I don't have experience with AMS-MAN flights, but e.g. when flying RTM-LHR this flight is operated by KLM Cityhopper using a F50. This is also a one-class plane, but you are able to buy Europe Select tickets for it. When booking (in C class) there is a very visible note that this route is operated by a one-class flight so there is no seperate C-seating.

Now you may have some chance of an apology, when the route is normally operated with 2-class (KLM?) planes, and this was only changed shortly before the flight. The amount of miles needed for the upgrade should have been the same as if only SIN-AMS was upgraded (which in effect was the case here).