> Just two extra instructions. No need to memory map or hard code the size of bounds.

Pretty neat idea! [Although the (register) dependency chain looks a bit nasty. 'and' will need 'sbb' to commit and 'sbb' will need to wait for 'cmp' to commit (flags register). But I guess the few/rare cases where this latency is really an issue can be dealt one-by-one basis.]

> No need to memory map

Well, using MMU can have performance benefits. Less repetitive bounds checking code and better performance in most scenarios. Both solutions have their strengths and issues, there are no silver bullets.