Generally speaking your holster should hold the gun snuggly enough that no additional retention is required. However, if a person were running, riding ATVs, riding horses, rambling in the woods, etc. a retention device might be helpful. Also, some departments require them, but I assume that is not an issue in your case.
At the end of the day I have no personal experience with the specific holster you mentioned, but would generally go without the thumb break.
A major source of objection to a free economy is precisely that it ... gives people what they want instead of what a particular group thinks they ought to want. Underlying most arguments against the free market is a lack of belief in freedom itself.
- Milton Friedman