This question has no right or wrong answer. It's a matter of individual preferences.
Back in 2009, my wife and I got a pair of ScubaPro Galileo Luna's. We've had excellent results with them.
I don't see the need for an SPG, nothing wrong with having them... in fact, I've got one as a backup in case I need to tap into it. Relying solely on AI hoseless works very well for me. This may likely be the case with several other divers.
Last but not least, even though it's common for crew members to switch tanks while you are on a liveaboard, or when enjoying a dive vacation, I'm one to explain on day one that I welcome their help and support, but have this obsessive compulsion to do it my self. They understand and let me take care of my gear. Never had a problem and plan on keeping it that way.
If you are hesitant, you may want to use both for a while and see if it's reliable enough for you just go with AI.
I currently dive with 3 computers. This is for sure an overkill, but that's what I like and that's what I do. I use the Galileo Luna, a shearwater Perdix, and a Mantis2. BTW, both Mantis2 and Luna share the same transmitter, so it's awesome.
Cheers,
Ricardo