doridori wrote:Just joined this forum, so please be kind to me

We will, provided that you observe the forum rules. (Location, location, location. Meaningful, meaningful, meaningful.)
It's just at the top of this page.
It's on the portal page.
It's in the
FAQ.

And, yes, welcome.
Has anyone used any of these? any opinions?
Yes, and yes.

I have the Nikon version of the Sigma, and it's a great, fun lens.
That said, there's not a very big price differential between the Canon and the Sigma, and with only a small saving, the Canon would be the better purchase. In the Nikon world, the Nikkor equivalent is substantially more, making the decision-making a different process.
anyway i just wish to use this lens just for some extra width, such as for indoor occasions
For indoor "occasions" none of these are what is needed. Rather, look towards the 24-70 lenses, or the kit or 50mm lens, both of which you already have.
These are, however, great lenses for landscape/outdoor use, and indoor roomscapes. They're often too wide to be used with the typical flash head too. Indoors, think tripod, full room, available dark.
And yes, distortions are a given. That's a part of the fun of these.
It may be worthwhile scanning the for sale section here, too. I think I may have seen somebody selling some Canon gear, including a 10-22, perhaps in just the last couple of daze. If you are unable to post in that section, PM.

g.
Gary Stark
Nikon, Canon, Bronica .... stuff
The people who want English to be the official language of the United States are uncomfortable with their leaders being fluent in it - US Pres. Bartlet