I'm taking the refund and will be spending it elsewhere. There was no offer of a half way and the price they offered the new one at was about par, could find elsewhere cheaper.
That's a shame, but in their defence they may be caught in the middle, it could be they got the old stock cheap and offering a replacement is in effect subsidising your cooker, even so I'd have thought they could offer something as goodwill. As you've already had some dealings with the manufacturer might it be worth appealing the their goodwill? You know the sort of thing, how you'd been looking forward to having one of their cookers, how the delay has caused all sorts of inconvenience...
I'm pretty sure in the first 30 days your only option was to reject. I've only dealt with similar in a commercial capacity, the rejection terminates the contract unless negotiated otherwise. You can then pursue them for any losses that result - I've been on the wrong end of that, supplier is liable even if the failure was due to another party.