Any significant difference between T-10 Thinner and mineral spirits?

[austinrick]

Epiphanes recommends their brand paint/varnish thinner, "...or a good quality mineral spirit..." for their high gloss clear varnish.

If I happen to be buying Pettit/Z-Spar T-10 thinner to use with Pettit one part polyurethane topside paint (#3175), is it okay to use it with the Epiphanes varnish, too? IOW, is it just a good quality mineral spirit?

Should I save the $$ and just use regular mineral spirits to thin & clean up both the paint and varnish? $19 for a quart of thinner does seem outrageous.