Thank you I was looking to buy the 18-200mm f3.5-6.3 II just for an all round lens instead of the kit lens 18-55mm from canon and maybe a 50mm prime lens from sigma also
Do you own a Canon body already (is this an "upgrade" to a new body... or will this be your first camera body?)
Canon (and the same is true of Nikon) don't publish any specs for the camera/lens interface. Companies like Sigma, Tamron, Tokina, etc. "reverse engineer" that interface and they test their work by checking to make sure everything works on all the camera bodies they have to test. This tends to be pretty good. But just occasionally a story comes out about an "old" 3rd party lens that won't work on a "new" camera body. That usually means something changed and the newer camera is taking advantage of something that the "old" lens didn't know about and was never tested for. This is not very common, but just occasionally it happens.
A bit about 18-200mm lenses...
These lenses fall into he "super zoom" category. You want one lens that covers all the focal lengths so that you don't have to swap lenses. DSLRs have "removable lenses" specifically because no one lens is ever the "best" lens. The ability to swap lenses gives you the ability to use a lens which is more optimal to your shooting situation.
For years, "prime" lenses (a "prime" lens is any lens that does not "zoom") were king and zoom lenses were... well... they were crap (all of them.) Pro shooters generally avoided them, but they sure were popular among consumers who wanted convenience. That was then. Fast forward many decades and the lens makers have learned a thing or two about how to make better zoom lenses. The high-end zooms have managed to get so good that it's getting hard to tell the difference between a prime and a zoom.
But this doesn't hold true of all zooms. It turns out it's easier to build a "less ambitious" zoom (which is what I call a lens that has a 3x zoom range). Divide the low number by the high number... e.g. 24-70 you'd divide 24 into 70 and discover that it goes in just shy of 3 times. So I call that a "3x" zoom (not because the image size is 3x life size.. but because the 70mm end is 3x the 24mm end (and yes, I'm rounding.)) A 70-200mm... that's another "3x" zoom (70 x 3 = 210... close enough to call it 3x).
If you push that to 5x... you're still probably doing ok.
But when you push that to 10x... now you're being REALLY ambitious. An 18-200mm lens is roughly an 11x zoom range. That's pretty aggressive. It's VERY HARD to make an 11x zoom and actually maintain good optical quality.
This is not to say an 18-200mm is no good... what I'm really trying to point out is that it's advantage is the CONVENIENCE. If you're traveling and have limited space to pack gear and you can only take ONE lens... that 18-200 might be your best choice. But if you're NOT traveling and you don't "need" the convenience, than your single 18-200mm lens isn't going to compete (optically) with what you might be able to do with a less ambitious zoom... and certainly won't compete with what a "prime" lens can do.
Selecting lenses is ALWAYS a game of trade-offs.