I am a familiar investor, and I use them to park cash. I don't see the harm, personally. Bit of fun, as long as you are fully aware of the return, or lack of, that they are accompanied by
this is a fair comment - IF you've maxed your ISA limit for the year then you'll get a similar (expected) return from premium bonds as you would from savings + tax... realistically you've got a high chance of getting a lower return still and a very very small chance of getting a ridiculously massive return.
(assuming you're a 40% tax payer - which is fairly likely if you're saving over 10k a year.)
