MOST digital pedals have that delay. BUT the ME-50 has a great trick included that at least some of the others don't have - if you change complete saved combi patches then yes, there's a delay (shorter than many other company's delays though). BUT if you just use it like it was originally intended to be used, which is to emulate a distortion pedal, modulation pedal, delay pedal and variable (eg: wah) pedal of your preselected choice, then you can turn each pedal on and off in real time without any delays. Used like that, to truly replace stomp boxes in a simple configuration, it has no delays and sounds great.
Also, the fx engine in the me-50 is the same as the gt-6 and gt-8 or whatever they're called by boss. Just that it has no amp/speaker emulations and is intended for a completely different audience - the me-50 is for people who prefer to easily turn knobs and hear realtime feedback to find their tone, not for people who want complex saved programs. It CAN work that way, but it's not why it was designed in the way it was. Why do you think it's more expensive than many other boss units? because a lot of money went into making a digital pedal work EXACTLY like classic analog stomp boxes, and no other fx box does it as well (not even that fancy VOX board you can buy, although you do get great vox amp emulation with that one which is the best part about that board IMHO).
me-50 is a different audience, players who want to play but don't want to know if the delay they just dialed in and think sounds good is 232ms or 242ms. You just dial it in, save it and it's there when you need it.