I find it interesting that MM calls their OPTs "Tone Clones" when in fact, they always shoot for an "improvement" over OEM. It sounded like they were trying to tame some of the top end hash with their Marshall OPT. I noticed the opposite with their Fender OPTs. I've used MM Vibrolux and Twin iron and didn't care for it in Dumble clones. It seemed liked they extended the frequency range which made the amp difficult to voice. However, when I pulled the iron and dropped it into a Fender circuit, the results were really impressive.
When all is said and done, you could probably voice the amp around any of those OPTs (or maybe just adjust the tone controls). MM's warranty is certainly a consideration if you're an amp builder, but honestly, I don't think Moss has replaced more than two OPTs in the last 5 years using Heyboer exclusively.
IMHO, yes...MM does have a lot of hype, but that doesn't mean it's not a quality OPT.