I'm in need of a 5 string, though if I get a 5 a 6 wouldn't hurt. My first thought was to grab an inexpensive Ibanez sr and change the electronics. Going that route will cost the price of the instrument plus $600 for pups and pre. So about $1000. I enjoy the btb's. They feel nice and play well. I've never had the opportunity to play a Mayones but man it looks amazing. I just dont know is it is worth double the price. I will say aesthetically I enjoy the Mayones more. It almost looks like they come from the same factory. How do the 2 compare in sound? They seem to be similar in quality. Here are the 2 in question. The 3rd option is an Ibanez 305 with a complete overhaul. Tuners, pickups, electronics and possibly bridge.
How much is money a factor? If you don't have to do something silly like max out a credit card/go into debt, I'd suggest giving the Mayones a whirl, largely because I have been lusting for one myself (not the model you've posted though...a Jabba in my case...) If money IS a big factor, and especially if you can do any/all the upgrades yourself, going with the cheaper Ibanez might be smart. I can't compare tones, but for three years I owned a mid-2000s Ibanez BTB 6-string with a bolt-on neck, and although I found it slightly bland tones-wise (something that I'm sure could have been remedied easily), to this day that bass remians one of the best I have ever had. I can't remember any build flaws, the neck was insanely comfortable, and the thing would stay in tune for months.
Money isn't the issue. I don't purchase "wants" on credit. I do believe in value though. The BTB I could get through GC and have that great return policy. It's hard for me to want to take a chance on a multi thousand dollar purchase. Maybe I can find a vendor with a good return policy for the Mayo.
It would be hard to go wrong with the BTB, in my opinion, but yeah, if you can find a Mayones through a place that has a good returns policy, that would be tempting...