I have line trained new copilots from MPL as well as non-MPL ab-initio courses as well as "self-sponsored" pilots. Due to different selection/aptitude criteria applied over time it is not possible to attribute differences to the method of training alone. I couldn't say that I found any obvious differences between MPL and non-MPL trainees but some correlation between a higher number of simulator sessions and subsequent performance on the line. Most of my trainees had close to minimum hours (around 200, MPL even less) and I don't consider that a problem. The US 1500 hour requirement is great from an industrial point of view as it raises the bar for joining but there's nothing in it that grades the quality of those hours between training and employment. They can give you great experience but do not necessarily. I had more than minimum hours when joining myself and would not miss those hours, although I consider the VFR cross-country hours more instructive than most of the towing. While not the best way to learn, narrowly avoiding killing yourself when flying alone does have a training effect.
When MPL was "invented" I always thought that the general idea of a mission-tailored training is good, but that I'd only recommend it if offered by a large, respectable airline. Having seen hundreds of Lufthansa MPL students "stranded" somewhere along their MPL path I would not recommend it at all unless accompanied by a "convert to ATPL" guarantee by a training Organization "too large to fail" or structured in a manner that would allow you to convert to conventional with minimal cost (some ATOs seem to offer that).
You need to understand that converting your MPL to another operator's MPL is a major effort for the new recipient's training department which only makes sense if they need a lot of pilots. There's no sense in establishing a conversion syllabus/programme with the authority for just one or two cadets.