I don't think $10 is too much, if you can afford it.
We all have different budgets with different priorities.
I spent about $20-30 on each OOT bag, so that is $10 per person. Because of that, I chose to do little favors, bottles of sand.
I also only had 30 guests, so the totals weren't too bad. I could not have done the same things if I had had 50 guests.
If you are using them as GM gifts, them I say go for it! They suit the theme and you could actually get a set for their house instead of just one.
DH was recently in a wedding and he got monogrammed golf tees as a gift. They were nice (and expensive) but I don't know how much use he will get out of them. The mug would have been a lot more practical.