If there's TFs in the game that give you choices...then it's not really about randomness now is it?
It's
intended to be about random TFs because that's Fenoxo's fetish... but most other writers aren't really into that (something which annoys Fen to no end), so over time, more and more TFs written by other people have been added with some degree of choice to them.
Also, the whole "getting duds when there are still available TFs" is due to how those specific TFs are coded; they go down a list, one by one, and roll for each TF before moving onto the next (or simply ending if the TF limit has been hit), and if you're unlucky enough to roll negative on all potentially valid TFs (which gets more likely the more you're TFed appropriately), you get the dud message because that's the last thing on the list and is what gets outputted if no TFs occur. Fortunately, that's not a problem for
all random TFs; others use a system where all potentially valid TFs are indexed into a list, and that list is drawn from randomly without replacement until either the TF limit has been hit or there are no more TFs to draw from - duds only occur if you're genuinely ineligible for any possible TF.
As a side note, I think the former system mainly applied to earlier TFs, while the latter is mainly for newer ones.