If you told Jim mains a year ago that we were going to get a parallel investigator's instrument, they probably would have joked that it'd be Duke and not Jim's trumpet reworked. Please think of them when you use this card to heal horror without a skull or hand slot.
On the face of it, Pete's guitar seems incredibly strong. It's a 0 XP, slotless, testless, actionless card that can be used outside of your turn. It's hard to draw fair comparisons with other cards that either take up slots, require a test before moving, or both.
Move a non-elite enemy at your location or connecting location: This can be triggered after Hunter enemies move, but before they attack (player window 3.2), so you can either use it preemptively or as a last resort before the enemy hits you. It's easy enough to see this ability being useful in a few ways:
If the enemy does not have Hunter, then moving it to a location without investigators can remove its influence without putting it back in the encounter card rotation. Just don't do this with Cultists.
You can choose a connecting location, so if an enemy would hunt to you or another investigator you can push it further back. If that doesn't work, you could let it move in step 3.2, then move it to a location without investigators before step 3.3.
There is no engagement requirement, so you can move an enemy off of one character and onto the fighter, or just move it off of them altogether. There also isn't a non-weakness requirement for anyone with an enemy weakness.
This effect can work wonders in solo when you frequently only have one enemy on you, or in multiplayer where there is almost always an enemy annoying somebody.
Then clause: Due to the flexibility in the timing window as well as being able to move enemies that are already not on your location, this will often happen without much effort. It's hard to imagine many decks that don't benefit from a passive resource option or healing horror. Honestly the guitar would already be strong if it just moved enemies around, the horror and resource are just icing on the cake. At least Jim will always have Flute of the Outer Gods.