FWIW, I think the information you glean with probe in cube is often a lot weaker than in constructed. Simply because any cube deck will have 23 unique spells versus a constructed deck running multiples and half that many unique cards? On the peek, some decks can be spotted easily (RDW... uh oh...), most decks I feel though are somewhat mysterious. So seeing someone's hand with a bunch of stuff in it might tell me little about how the deck actually plays or what it's ultimate goal is. Maybe I learn about colors (all they have in play is an Island but they also have red and white cards in hand). This is less true in combo focused cubes clearly where build arounds give away what your deck focus is, but in a midrange list? Every deck looks similar. So other than seeing a counter or removal spell or whatever (that I need to worry about interfering with my game plan in the next couple turns), is anything really being spoiled?
I would argue that in constructed you usually figure out what deck someone is playing just by like, their Turn 1/2 plays anyways. The value of the information is in knowing whether specific cards from that archetype are among their holdings.