After much searching and trying out of tea infusers, I find this type the best, and this one is a bit bigger than most, giving the tea leaves loads of room to move while they are brewing. It's also an attractive-looking product.
Fits most mugs, only it is a bit too deep for quite small/shallow cups or mugs (e.g. in my extensive range of mugs I have one type which it is too big for). However, overall I'd say the bigger size is more of a plus than a minus, means it can be used in a teapot as well and I prefer slightly larger mugs anyway.
The holes are very small both on sides and bottom of infuser, which is important and where many infusers fall down.
Basically, buy it - it's great!