Killer is often criticized for not adding much to a laptop beyond some extra cost. The benefit Killer touts is prioritizing latency-sensitive traffic, e.g. for games. I haven't used one and can't say how effective they are, but suspect it is true that for most people, the difference wouldn't be perceptible. The software might be more efficient, but it isn't going to make the radio waves travel any quicker.

But I haven't heard about reliability issues, and as long as that's the case the worst outcome is paying a couple extra bucks for a fancy WiFi card with no difference/a small enough difference you can't notice it.