I recently bought a Millennium 5 Plus here on TB, but the seller found some electronic issues with it and refunded my money (still hoping he'll sell it to me with the issues, and I'll just have them fixed myself, cause I REALLY wanted that bass...)
However, I currently have an Axcelerator Plus 4 string and love it to death - I found a 5 string version in a matching color (only difference is it has chrome hardware, and my Plus has gold), and it's about half the price of the Millennium. That being said, I haven't played a lot of 5 strings, but really want one for variation in my studio, I know the Millenniums are using different pickups and preamps, different body woods and they have a longer scale (34" vs 35").
I'm totally happy with my Axcelerator Plus as a 4 string, the tone is beautiful and it plays amazingly well, but I'm not sure I really want to get a 5 string that sounds pretty much the same (the Plus and 5 are different body woods, so I'm sure there's a difference, but how big a difference, I'm not sure) - The reasoning behind spending more on the Millennium was that it has a J/MM setup and different electronics, as apposed to the soapbars in the Axcelerator. People coming into the studio could choose which they liked the sound of better, and if they're playing 4 strings for their songs, they don't need to use the top string on the Millennium, if they liked it better.
In your opinion - Is the Millennium Plus worth twice the money (or more) over the Axcelerator 5?
No, I can't try the Axcelerator 5 before I buy it, nor can I try the Millennium.
FWIW, this will likely only get studio use only. DI'd directly into my mic preamp, with a second track going through a SansAmp RBI. Mainly doing rock and metal, so a more aggressive sound is preferred. Cheaper definitely appeals to me, but I don't want to buy two instruments that sound essentially the same, or regret spending money on something cheaper, when I could've gotten something much better, still within my budget.