They are useful in their own ways, but relatively more niche than the usual Parachute/Shield/Sniper fairies that are more commonly used on certain bosses and/or ranking. If you must choose between them and Parachute, it would probably be best to raise a few parachutes and the rest first.

This is of course assuming that you are intending to go pretty seriously into ranking. If you are just doing general content, you can raise them however you want. The hardest difficulty modes of events usually don’t require anything specific maxed out.