'of' vs 'from' operator

Not quite. When passing an array to Observable.from, the only difference between it and Observable.of is the way the arguments are passed.

However, Observable.from will accept an argument that is

a subscribable object, a Promise, an Observable-like, an Array, an iterable or an array-like object to be converted

There is no similar behaviour for Observable.of - which always accepts only values and performs no conversion.

It is important to note the difference between of and from when passing an array-like structure (including strings):

Observable.of([1, 2, 3]).subscribe(x => console.log(x));

would print the whole array at once.

On the other hand,

Observable.from([1, 2, 3]).subscribe(x => console.log(x));

prints the elements 1 by 1.

For strings the behaviour is the same, but at character level.