Anyone out there with experience with this mouse? I have a 620 but lost the dongle. I was going to replace the 620. Is this worth the money? Does it have a power switch in the bottom? Can the dongle be stored with the mouse?

Thanks!

Power switch yes, dongle storage no. Nice mice otherwise.

This is a great mouse, worth it just for the micro precision wheel. The wheel is balanced and when spun switches from 'click' to free spin to quickly scroll down those long docs or web pages. Don't hesitate at this price.

Normally " dongle be stored with the mouse" is for mobile/notebook mouse -not really for desktop mouse.
It's a great mouse you won't be disappointed. But the price wise- not really great. I got 2 for my client for $19 AR last November. But now days - I will say under $30 then it should be a good deal.
However if you don't want to junk your mx620 ( I think it is not really old and cheap, isn't it?) - you can always email Logitech support and ask about replacement dongle- the support will email you part number and also price. It should be around $10 ( price may vary depends on model- not sure about shipping) or you can get the part number and search on ebay for it.