I'll throw my $.02 in since I've been using the one that came with my bike when I purchased from the previous owner.
It's a great unit and money well spent - especially since my bike didn't come with any type of bike computer. I was spoiled on my orange 300, that kept track of mileage, hours, etc. I missed having this on the GG and getting the Voyager working was a bonus.
I think the biggest drawback for me is the inability to load TOPO maps (not sure if the current model allows this - think it was talked about when I originally checked, but don't know). I purchased a Garmin 60CSx to track rides and routes when I first jumped back into the sport and still use that as my main GPS logging/mapping/route planning tool.
The ability to load tracks and keep logs works very well in the Voyager, but without the reference of a topo map, it didn't work all that well for me. If this has changed (and you can load maps), please disregard - haven't checked into it in over a year as I use my Garmin.
It might not be that big of a deal in your area, but where we typically ride, there are tons of logging roads and spurs cutting between trails - the ability to "see" these really helps when trying to figure out where the heck we are in the woods (lol).
The only other issue I've encountered is battery life - not so great. It would be nice if they made their system to hook into the power generated to run lights, etc, but I learned that even though their documentation used to say to do this, their support folks said not to as it fries the circuit - and it did it to mine. That said, their support folks are outstanding and they shipped me a new unit when it was determined that it was toast.
I rely on mine to keep track of mileage, engine temps, etc and it's great for that. A bit overkill given I don't use the mapping function, but it's a great unit and I haven't had any issues after setting it up for (internal) battery power only