They're really good with no awful side effects or tastes. I like some vegetarian options, but honestly, most of it either tastes nasty or has poor texture.
My girlfriend dislikes some meats and seems to want to be a low-meat household, she loves morningstar nuggets of most kinds. Another good one is Quorn. They are a cultured fungus protein and it just makes a much more meaty tasting and feeling product, and you could easily forget it's not chicken.
Big problem though is the required level of processing to take a vague protein slurry and turn it into a glued together nugget means it's only really comparable to the absolute lowest quality, bulk batch, school lunch grade nuggets.
Quorn is a fermented slime mold, the fungi label is a marketing trick.
This said, I used to like Quorn before they started stuffing egg (mostly eggwhite) into everything. The real slime mold is great, but where I live it's near impossible to get Quorn products without the egg. They taste as bad as impossible/beyond with their clearly chemical taste.
Going beyond this, mosr vegetarians/vegans find over time that it is much cheaper and actually nicer to go simple, not with the replacements. tofu, seitan or simply vegetable dishes without any of these things. E.g. in a well flavoured bolognese/ragout no one can taste a difference between meat, fake meat or simple hard tofu (mouth feel/texture are clearly different though). And anyone should really try making seitan, it's super fun and easy - basically you just wash a bag of flour repeatedly with warm water.
I realize they are processed food but I really like Morning Star ~~Farms~~ Laboratories products. No one is going to mistake their products for meat but they are still delicious.
And I doubt their business is struggling, or that Beyond Meats's fate has them worried.
They're really good with no awful side effects or tastes. I like some vegetarian options, but honestly, most of it either tastes nasty or has poor texture.