Why would I buy one when 99% of the time my anchor comes up without issue and...when there is an issue it is sorted in minutes?
No, not just luck.
It all depends on the setup. Some seem to have no need for a swivel, others benefit from one. That's why I'd suggest trying without one first and only add one if needed.
I agree.
We've been anchoring 5 to 6 days a week, 2 to 3 months/year for almost 30 years.
We tried a variety of swivels at various times to reduce chain twist. The swivels made no difference to the rode twisting or not. We have 3 feet between the anchor roller and windlass which allows me to lift the chain off the wildcat and twist it to bring the anchor onto the roller at the correct orientation.....A swivel reduces the flywheel effect. A deeper groove on the roller make a significant reduction in chain twist....
There used to be a program on TV, where the catch saying was..."I think the answer lies in the soil". in a rich Yorkshire accent...
I think with regard to this swivel v's no swivel the answer lies somewhere amongst all the comments...
I used to use one, then went without, and my experience was like Simi - came up right every time. I worked out it was because I always made sure the links in the chain were aligned right from the gypsy to the anchor shackle. I also came to the conclusion it was the nice groove in the roller that helped keep it all aligned, and this is clearly more effective if the chain links are of sufficient size such as to help guide the chain by fitting well into the groove.
So, in my view, the answer is not in the soil, but in Nomad Willy's comment below
With an all chain rode and a grove in the center of the bow roller one should not need a swivel or flip link. How could the chain get disoriented? If the groove is deep enough for the chain it should come up as it went down
...provided (1)one's chain links are big enough...and (2)the groove in the roller deep enough...and (3)you make sure there is no twist between the gypsy and the anchor. Also (4)it will tend to not work in mixed rodes where at least some rope rode is run out.
So, unless all those parameters are met, it won't work as planned, which is why so many find they do need a shackle. That's my take on it anyway, and I thought about it a lot before I had the courage to drop the swivel out. Especially now, when I no longer have a boat, and the thing I miss most is going out and anchoring, strangely enough. I really miss my Sarca. it worked perfectly...the boat overall, not so much.
I also agree it is quite possible to have a shackle that not only does work, but is strong enough not to be a weak link, if you are one of those with the issue not solvable by being able to meet the 4 parameters I mentioned.