Some Museum are large and some are small.
I think MG series figures are smaller than Ess*x, most especially the horses. I think the PR series are large. I mix the PR series in with Ess*x and find, to my mind, they fit well.
On the other hand some of the PR figures are midgets on massive horses.
All of the Museum cavalry are one piece castings
Some Museum horses are crap, some are very nice. Lots of the figures are illustrated at the Museum website.
The AC range I would say are definitely sized with Ess*x but I don't like most of the horses.
The PR range seems to be Islamic Persians and the MG are pure Mongols.
But both are mixed on the Museum webpage in the same lists.