The Vortex bomb series is a synergy weapon rather than a damaging one. Much like the Pulsar series it is made for controlling where the enemy is. Pulsars are typically used defensively to hold back enemies and to push them into clumps.

Vortex Bombs are much more offensively synergized, that is they are used to help increase the damage output of other weapons. The Electron Vortex is typically hailed as the best but the Obsidian crusher also finds much use in levels where healers abound (arenas for example). The Graviton Vortex is the easiest to obtain and deals more raw damage on the blast but the status on the others make them much better offensive support tools.

If you are planning on using vortexes you must have decent CTR on them (via armor, trinkets, UVs, or sprite perks) and on other weapons as well. The radius of affect is smaller than any other 5 star bomb and the walk speed is slow so practice is a must.

If you can't get good CTR on all your items (you need to be able to charge your other weapon before the vortex blasts) then be sure to bring teammates who you can work with and can take advantage of your vortex.

PS
Vortex bombs work wonders in compounds when paired with the Voltaic Tempest.