Mass laws aren't in strange legalese, the only problem is that certain parts are vague and there doesn't seem to be much case law.
I don't know what they refer to here:
"...or a device or case which enables a knife with a locking blade to be drawn at a locked position"
Anyway you can find the full law
right here. Scroll down to (b).
I'll sum up Mass state laws as best as I can:
You cannot carry on your person or under your control in a vehicle:
Stilettos
Daggers
Ballistic knives
Dirks (ie push daggers or basically other daggers)
Double-edged knives
Automatics with blades more than 1.5" long
Various other things like brass knuckles are prohibited in that paragraph as well.
I don't have a link directly to the Boston law on a Mass. web site, but you can
see a copy at Bernard Levine's site. Scroll down.
Essentially, no knives over 2.5" unless you have a reason for it. There's also a blurb that prohibits any object or tool designed or intended to be used to harm people. So if you have an encounter with the police, you'd better make sure that they know your knife (or anything else) isn't a weapon.