Their performance got the attention of the Administration, and Lincoln subsequently pushed procurement of the Spencers for all the Federal troops. Our people called those weapons the "Yankee Seven Devils" because of their multi-shot capability. (Actually, they held 8 rounds; don't know the reason behind the "seven" unless it's a Biblical reference.)
J.E.B.Stuart was off joyriding when the Battle of Gettysburg started -- deprived Gen. Lee of critical intelligence information when it mattered most.
Only if you were willing to carry one of those rounds in the chamber while you were riding - a potentially dangerous move.
Apparently most cavalrymen kept the chamber clear until they engaged, giving them seven rounds before reloading.
That's a common misconception. Buford's Division was armed with a single-shot, breachloader made by Sharps. Repeaters were not standard issue.
A single Regiment of Michigan Cavalry was armed with the Spencer at their colonel's expense. These troopers were not part of Buford's Division, nor were they involved in the meeting engagement of July 1st, 1863.