You can screw through the stud even from the shared stud. Just go from an angle from above/below. The Kreg just predrills for you to toenail. You can still toenail if you want without the Kreg. Just won't be as pretty and may split the face of your blocking (won't affect structure).
When drywalling, put some drywall screws into your blocking and it will help lock it all together.
Marantz SR7013, Polk Signature S60s/S30/S15s/HTS12s, Polk MC80 (x4), AC Infinity T9/S9, AAB4 HTPC, Panasonic DP-UB420K...still to come - 82"-85" 4K QLED or eqv.