Well the audience has no idea how minds are "supposed" to be read, so its perfectly exscusable and perhaps even preferable if we use pendulums, crystals, etc. to "aid" the process, if only to add a bit of realism.
I think the amount of props does not really affect your mentalism, as long as what your audience sees is not your paraphernalia, but your MENTALISM.
If I was the spec, I wouldn't want to see you take out a notepad, treat it like something special, make me write on it, then wait while you read the impression I made on the notepad. What I want to see is you reading my mind, plain as that.
If your audience only sees props you want them to see, then that is the amount of props that you will want to use. If they see more than necessary, screw your props...or rethink the amount of stuff you bring to a show. As D ICE R said, he IS his favorite mentalism piece, because mentalists are Mentalists, not guys with props.
If you are performing Mentalism professionally every time you pull out a prop your price goes down. Becuase if we could actually read minds, then we could have someone just think of a number, and tell them what it was. People associate performers with playing cards as someone who is going to have them choose a card, then find it. Not someone who is going to have them select a playing card and tell them what it is "Through mind reading". When was the last time you had someone hear you can read minds and go "What card I'm I thinking of?". Cards have no meaning to people outside of a gambling context. The only reason someone would care about cards is if you are doing a gambling demonstration or showing them their pre-concieved notion of what a card effect is. If you could really read minds or predict the future, why on Earth would you use playing cards? Why not make it more personal and have them think of a loved one, a special date to them, something they actually care about.
I would say that mentalists who manage props well can mitigate this. As long as the props are innocent looking and examinable, I don't see why this is an insurmountable problem.
People associate performers with playing cards as someone who is going to have them choose a card, then find it. Not someone who is going to have them select a playing card and tell them what it is "Through mind reading".
The invisible deck/brainwave deck as well as a number of Max Maven's creations are mentalist effects with cards, and they do look like "real" mind reading. Your audience might initially think this is just another card trick, but an experienced mentalist can slay them with these classics.
If you could really read minds or predict the future, why on Earth would you use playing cards? Why not make it more personal and have them think of a loved one, a special date to them, something they actually care about.
That's fine, but playing cards allow you to explore a number of themes/presentations besides just the gambling related ones. That is why the magic literature seems to be dominated by card magic. As a mentalist, why would you willingly ignore such a large part of the literature? Why not explore the literature and come up with presentations that make the audiences care about playing cards in the mentalist context (Out of this world is an example that comes to mind)?
Something I do that uses cards and is strong is to have someone think of any card, and then to have another begin dealing down cards and then to stop at some point when it feels right to them... the card they stop on is the card that the other is thinking of.
That is a very brief description but when done using two friends or a couple, and to have it be about the connection between the two of them, this plays incredibly well.
The effect happens completely out of your hands and the thought of card is only known to the person thinking of it.
I have never seen Derren's DPB so wouldn't know, though they could be similar... mine doesn't use any sleights and such, I wanted to be able to perform it without ever touching the deck at any point, it needed to feel and look as clean and 'real' as can be.
Aswell as using playing cards I would also use someones photos, or have one imagine something and the other draw it... this is actually how I use it now.
The presentation is actually a big part of the method itself when doing the playing card version, as you need to cause the participant to feel certain emotions for it to work, though there are easier ways of doing a similar effect but I wanted no gimmicks, no set-up, no need to touch the deck at any point ever. It's not at all about what I can do, it's all about them and I want them to actually experience this deep connection between them with the cards being nothing more than a veichle to help deliver them to this destination.
Really we can use anything we wish to achieve a desired effect, there are no right or wrongs or best and worse ways, just as long as it fits you and your presentation... you could even use spongeballs and by simply framing the effect as hypnosis and influence you would have something that would feel completely different to how it usually would.
I don't do the above but just saying that we shouldn't limit ourselves.
Now I have my own feelings about what I like and how I go about things, but everyone should do what feels right to them and not be influenced by whether others agree or not etc.