I was listening to the rational reminder podcast recently. (Episode 129 About Fama French Five Factor Model Portfolios for Canadians) and they'd mentioned at the end of the episode that XUU had developed a significant tracking error in comparison to their underlying index benchmark in 2020. (One year tracking error ending November 2020 XUU returned 14.12% vs it's own benchmark which returned 15.42%).
Episode link:
https://rationalreminder.ca/podcast/129(fast forward to 59th minute)
To me this is a significant permanent lost due to the fund management execution error with no guarantees that they will do something about it in the future. Yes you will pay a bit more in MER fees with Vanguard's VUN, but 7 extra basis points a year vs a tracking error of ~130 once in a while is totally worth it in my opinion.
Furthermore running XUU vs VUN via portfoliovisualizer.com
Shows that VUN exhibit slightly lower volatility with slightly better annual results in each year starting from March 2015. This slightly better return yoy so far has been compensating for a slightly higher management fee :)
I know that past returns do not guarantee future outcomes, but nevertheless it is something to think about.