Typically the 83b is only helpful when the strike price is low enough that exercising is "cheap." Once a company raises its series A, exercising crosses ~$50k, and the risk is too high for most people.

Relatedly, you can spot a bad startup by them refusing to let you 83b early exercise. It's a pretty clear sign that either the founder or the investors don't have the sense to care about their employee compensation, and probably they're being pound-foolish about a bunch of other things too.