Never seen the point of them. There was one in a holiday cottage we once rented and used it for novelty value. Noticed it had taken the pattern off the tea mugs which were same as mine at home minus their pattern, yet failed to properly clean curry pans. Thus, it (excessively and damagingly), cleaned the stuff that was easy to wash up by hand but didn't actually clean anything dirty which you had to hand scrub anyway. Likewise in another holiday cottage someone put my good knife in the washere slighlty damaging the handle and totally trashing the edge which needed 20 mins to re-sharpen. And at home my super duper copper saucepans mustn't be dishwashed apart from my good knives.
Total waste of time - even if they actually worked and didn't ruin your good stuff and fail to clean amything dirty, by the time you've loaded and unloaded it you may as well have done the washing up by hand
We dumped the one that came with our current house as a cupboard was clearly more use.