There is a 180 day key reveal deadline

This date starts at the date of purchase, there is no guarantee keys will work past that date either(still collecting data on how many keys have been revoked past this deadline)

You can adjust the amount that goes to charity

Just like with Humble Bundle, default split is ~30% to GMG, 5% to charity and 65% to the publisher, the box to adjust the donation is under the checkout button and needs to be done before checking out. The more to charity button will increase the amount going to charity to 15% or you can do the custom split giving the majority to to charity(GMG has a 15% minimum cut).

Putting more to charity may save you money on sales tax depending on your location.

Region locks

Games in GMG bundles have a high frequency of region locks(some bundles it's just 1-2 games, some it's everything), it is highly recommended to check the discussion thread for the bundle on SteamGifts to see if anyone reported what the region locks are if you are not planning to the redeem a game for yourself. It may take some time for the bundle discussion and region lock reports to come in.

If you are buying for yourself you should not have any issues, if you do have any please reach out to GMG support.

For other questions it is recommended to read their FAQ, this wiki page will be updated as needed