I bought a stock mostly original MB5 not too long ago. If its the same bike I'm thinking of it looks very nice and well cared for.
I think most MB5's that fetch a lot of money are in all original condition. Thats where the value is at. People love original and they will pay dearly for it.
Having said that if its Ryans bike...He has all the original engine and exhaust pieces not too mention a host of original documents. Basically, a super clean bike that can be made original or aftermarket.... Pretty ideal for me. I would have jumped on it, but I already have a bike and a car and I couldn't pull the trigger on something over a 1K.
Echo on what Briny said...."its a honda" My MB5 has been very predictable and reliable, but its also stock. I have no direct experience with aftermarket parts.
Ryans bike(if its his) gives you a lot of options. You could convert and sell the used parts or maybe the entire setup in a flash on this forum.
My premix is removed. Previous owner rebuilt entire engine at 2200miles because he was extremely thorough and enjoyed this type of work.
Its just something to go wrong. That kind of failure is detrimental to a two stroke. Any time I can eliminate a potential failure, I will.
Premix isn't that bad. The last time I put gas in mine I thought it was low...it barely took a gallon..Just keep a 3-6oz premix bottle with you in case...I use one I found at Autozone. Just look for a level/measurement indicator on the side. I usually have a backpack on anyway...so its not a hassle.
They also make SS fuel containers that look like a cylinder and hold a liter or so of fuel. Back up premix and peace of mind.
Premix will only be an issue if you do a lot of long trips...more than 80-90 miles a day.
Good luck. I think the MB5 is great. I think its not as fast as most people think it maybe, but very reliable.
Have you ridden one??