I can't think of anything else like avocado, but the secret is to eat them at the right stage of ripeness. If under-ripe, they are hard and tasteless, if overripe they look horrible and unappetising, and taste like mush. Inbetween they are velvety smooth and imho a totally luxurious taste experience (I'm biased obviously).
Would suggest you buy one and try it?
They need to be slightly tender to the gentle squeeze (but don't let the shop assistant see you squeezing all on offer or you'll be thrown out!). It may be that Tesco's have a pack of two which they call ripe and ready?
When you get them home, remove the stalk when you think they are just about ready. If it is green underneath the stalk, they are still unripe, if white underneath they are perfect, if slightly brown they are over ripe but most likely still be edible. If dark brown they have gone too far. You can keep them in the fridge at the ripe stage for several days, but the flesh once exposed will rapidly turn brown on exposure to the air, so wrap any unused half in clingfilm, leaving the stone in (how can you possibly not eat the other half.......). I eat mine happily just with a teaspoon and a sprinkling of salt, or I fill the hollow from where the stone was with balsamic vinegar, or indeed anything slightly savoury, like mayo, coleslaw, marie rose sauce or of course, anything you fancy.
They are full of good oil, fibre and vitamins and not too many carbs - I reckon on 9g per 100g.
Hope this helps - do hope you like them!