Pretty sure they're fine even though they're cheap! They were always accurate for my ovulation (even though I have mild PCOS) and I got my 2 BFPs using them. I'm pretty sure they're what the NHS use too.
I've just started using these - I'm on day 15 of an on average 35 day cycle. Showing no LH surge yet. It's the first time I've ever used these so I'm hoping they will show clearly when I am ovulating. This is our 3rd cycle TTC - fell instantly with our first. Putting a lot of pressure on ourselves and struggling to relax about it all. Only planning on tracking ovulation this month so I have an idea x