It depends on what you already have, your play style, and your squad power. Don't buy revokers yet if you don't have a plan for them (what mech to put them on). I'm no expert but here are some of my observations (considering only up to tier 5 for your scenario):
1. You have to get up-close, so squishy mechs won't do. Ares might be a good option for lower squad powers. Zephyr might also work, but since it has 16 energy capacity it might be best with revoker 6 + revoker 10 (which you'll get in tier 6 for credits). I've started to use it occasionally with my Slingshot. It's a weak mech, but the dash allows me to get right up to the opponent giving me full benefit of the revoker fire rate.
2. The aim has to be accurate. Unlike most other close quarter weapons, there's no damage spread, so it is easier to miss. For fast moving opponents, you need to either be right next to them (e.g. with Slingshot), or use minimal or vertical aim assist so you can aim a little ahead of their movement path.
Point 2 is not that important. It can be learned with practice. The main thing is point 1 - what mech you plan to pair it with.
I've not used Repeater so can't compare the two.
