Its only a matter of programming style than using an RTOS or not.

Agreed; however, those that come out asking blankly for a RTOS invariably use the programming style of "forget this is a '51" which usually lead to disaster (I have seen a few).

It is, of course, possible to apply the word 'multitasking" to a well desinged system with interrupts and, indeed, a statement in main() [if (active)] could be called task switching. The point that I try to make is that preemptive task switching in the form it is usually referred to is a disaster on the '51 since it will lead you to excessive XRAM usage which is a killer of '51 performance.

Erik