Oh come one you just keep changing the subject every time. Now you're selling a book cover so you recommend using a tripod
Of course it is prudent to use a tripod whenever possible, if the highest quality results are desired, and whether you're shooitng an SLR or RF or pinhole soupcan. But you just said above that you "doubt whether either [the Mamiya or Bronnie] would perform satisfactoraly handheld" and that was the statement that I challenged.
Perhaps we should find out what the OP means by "slow speeds" ? And then continue.
And yes, a cable release or timer is very helpful even when shooting handheld. Again, it's all about finger impulse, many people don't realize that.