Alkanadi:

antoniomoya:
Use your common sense. It's that simple.
"Manĝotablo" or "Manĝtablo"?
"Dormoĉambro" or "dormĉambro"?
Which is easier to pronounce? That's then the solution!

Both are just as easy for me. I think that other language speakers have consonant clusters, which would make it hard for me and easy for them or vice versa.

In those cases, both versions are easily pronounceable and it's optional as to whether or not you leave the o in. There is no rule as to when it must be included or omitted, it's always your choice. There are times when compounds simply aren't pronounceable without the o. For example, if you want to say "water bottle," akvobotelo is very difficult to say clearly without the o.

I think that whether a given cluster is difficult to pronounce or not is in the eye of the beholder (or the ear of the listener.)
Maybe for someone the (word-initial) cluster "vspl" is difficult, but someone else might say: That's easy; it's the same as in всплеск.

Nevertheless, if it is difficult to pronounce for you, put in a helping vowel to be on the safe side.