I think that the apples will take away some of the “spicyness” of the plain mincemeat.

Always keep the slow cooker covered for the specified cook time. Removing the cover lets heat escape, adding 15 to 20 minutes to the cook time. Only remove the cover if a recipe specifies and only after the first 2 hours of cooking.
An extra-large slow cooker is especially good for large cuts of meat that need a long, slow braising. A 5- to 6-quart cooker, especially an oval one, allow roast to sit comfortably with enough room for additional ingredients and liquids.
For even more flavor, before rubbing the roast, sear in a hot 12-inch skillet on both sides, just until browned. Transfer to slow cooker insert and continue preparing the recipe as written.
Leftovers? Shred the meat for tacos or serve with beans and cornbread.
Leftover brisket and sauce freezes well in an airtight container up to 3 months.