We used xytex about 4 years ago, had no issues with them very helpful and we have a child now!

Xytex has very large sibling groups (80 kids per donor is not uncommon). But then again, so do many others of the large US (and Scandinavian) banks.
The number of children from the donor within the UK however will be restricted to ten families.

I think Xytex try to keep to a 65 worldwide family limit... They don't export to the UK for home insemination so you can be guaranteed that the donor's family limit will be 10 as per UK regulation [unlike Cryos].

xytex import to the UK for clinic insemination though and respect the family limit of 10 within the UK. they still use that same donor elsewhere though - both worldwide and in the US.
I don't know that they have a US limit - they certainly didn't previously. I remember talking to a woman at zytex about average sibling sizes once and she said 80 was common. that was around five years ago. I'd expect that number to have risen as I get the impression that they are more up on exporting now.
I didn't know they had a 65 worldwide family limit- although that's still 65-130 children (most kids in my children's sibling group are one of two).

oh you're right! I'd just add that they seem to be judging the families by the number of people who report back to them. but in the US there is no requirement to report back to the sperm ban (unlike in the UK where all births have to be registered) which means they are keeping a track only on those births reported to them - so the actual family limit may be (much) higher.

"Although there are no laws or regulations in the United States regarding the number of children that can be conceived with sperm from a single donor, we have chosen to limit our donors to 60 family units worldwide. We track the number of children born and family units for each donor through pregnancy and birth reports provided by patients.
Although we place limits on how many worldwide family units can be conceived using a particular donor, families who have a reported birth by a particular donor may continue to use his supply even if he reaches his worldwide family limit, provided there is available inventory. The easiest way to ensure access to the same donor used to conceive your first child is to buy additional units during your initial purchase.
Additionally, our xyLimited Donors offer an even greater peace of mind by limiting the number of worldwide family units to 15 instead of the standard 60. We also offer an Exclusive Donor which provides a single family with access to a donor’s entire inventory, ensuring that no one else can conceive using his supply. This requires the purchase of all of the Exclusive Donor’s units.