I was an early purchaser of the Sigma and then regretted that I didn't buy the Tamron due to the tripod mount availability, well you can now buy Chinese tripod mounts for the Sigma.
https://www.ebay.co.uk/sch/i.html?_...1313&_nkw=sigma+100-400+tripod+mount&_sacat=0
You can also buy them for the Tamron at a lot less than the over £100 Tamron version
https://www.ebay.co.uk/sch/i.html?_...1313&_nkw=sigma+100-400+tripod+mount&_sacat=0
You can also buy them for the Tamron at a lot less than the over £100 Tamron version