Just to be clear, this is ESPP type for a publicly traded company? What are the EU rules for holding?
For me, at Fortune 500 company it’s been great. Not super sexy growth, but most of my lots are stable. And even lots that have lost value have not really fallen below the discount price. I think the challenge for me was the combo if ESPP as well as Stock Option and RSU’s quickly led to a place where I was/am overexposed to the company for my non retirement investment. You need to be disciplined to annually, or quarterly, selling shares and reinvesting to diversify.
On the downside, if shit hits the fan with your company, it sucks. You could lose your job and lot of value in stock if you have so much. That said, if you believe in the company and already have a somewhat diverse portfolio of index funds or other holdings, it’s probably a no brainer to opt in.