I've spoken to MST and can confirm that the weight allowance is the stumbling block, amongst other things.....
KLM 1 x 20kg plus hand luggage, excess at approx £25 p/kg

AA 2 x 23kg plus hand luggage, excess, what excess!!!!!
KLM flights only give 55 min connection, not much when you've got passport control etc to go through!!!!
AA there is at least 3-4 hours connection time.
Gary
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Did I mention that we have been to the Galapagos?
Yup we really did, took bloody ages too, but was worth it......................just