I started my dcs on high strength vegetarian omegas (made from farmed algae) earlier this year (around April) and we have seen big developmental leaps in ds1, who has ASD. Of course he could have been going to have those leaps anyway, but we definitely noticed a correlation between starting him on the oil and the improvements.
He's gone from never being able to sit still for even a minute during lessons at school to, when I took my youngest on a tour of the school the other morning, me observing him sitting perfectly still completing a maths worksheet. My jaw literally dropped open when I saw him, as I have copies of numerous classroom observations from various professionals that described him as constantly in motion and unable to sit still, let alone concentrate in class. He was so focussed on his work, that he failed to notice myself and his little sister standing in the doorway of his classroom for ten minutes - this would have been unimaginable a few months ago.
We buy Opti 3 which, being vegetarian, has the advantage of not tasting at all fishy - in fact it doesn't really taste of anything at all. The capsules are huge, but we snip them with scissors and put them on his breakfast or into a yoghurt or smoothie.
They have recently raised the dosage in the capsules and coincidentally (or perhaps not, who knows) both his teachers and his ASD inclusion teacher have commented on how much calmer and happier he's been at school.
For us, personally, I would say they are an absolute must. Obviously I can't prove its the omegas that have brought about the improvements in ds1, but I'm not going to risk stopping them just in case. They are by no means cheap and we can't really afford them, but now make it a priority for all 3 dcs to take them on a daily basis.
Bear in mind though, that we are a vegetarian family, so its logical to assume that ds would have had very low levels of usable omegas in his diet to begin with and therefore we were perhaps more likey to see an effect.
I also take them myself. Started back in April and by mid May I started to see big improvements in my CFS symptoms. Seven months on and I am well enough to do the 30 Day Shred, very different from this time last year, when I had already started to go downhill and ended up with 7 months of basically being housebound, even bedridden at times. Again, I don't know if it was the omega for certain - I have also lost a lot of weight and built my fitness levels up gradually, so it probably all plays a part, but as with ds1 - there's no way I'm risking stopping it to find out.
For us, we started to notice a difference in ds1 within the first few weeks, so its easy enough to buy a couple of bottles and give it a go. If you don't see any positive effects, you don't have to buy any more. We felt the improvements in the first few weeks were significant enough to stick with it and are now pleased that we did.