[RPG] What are the Rules of Hidden Club

D&D 4e and Essentals are completely compatible. They use the same rules and same basic ideals.

Looking at this review, as I trust the reviewer, it is better to say that the Monster Vault correctly obsoletes MM1. This is a very good thing, as the monsters in MM1 were, from the perspective of 3 years down the road, poorly designed.

Functionally speaking the only adaptation you will need to do is to older adventures which use poorly-designed monsters.

This is substantially correct as a summary of the numbers-based rules, yes.

The inference that Bluff is a vital skill isn't correct though. The Hide skill is used to avoid detection in the first place. It is possible, but very hard, to hide after you've been detected... but the game acknowledges that someone very clever and skilled could pull off a "vanishing act" like that after they've already been spotted, so it provides some rules for it. But using Hide after being detected is not the normal use of the skill.

A ranger stalking through the woods to scout out a forward position uses Hide to avoid being detected at all. A thief infiltrating a keep in the dead of night uses Hide to avoid being noticed by the guards on duty while they slip in and out. If they need to cause a distraction in order to hide again, it's because they've already failed at their primary use of the Hide skill somehow, and in such emergency situations "re-hiding" will not always be the optimal response. (Fleeing is probably much better suited to most situations.) Buying up the Bluff skill is far from necessary, as there are other ways deal with such a contingency. Investing significant advancement resources into becoming especially good at vanishing from plain sight while observed is only one way of dealing with it; a flavourful one, it's true, but an expensive and very specialised way of developing a character.