Once again Hasbro and joined with Humble Bundle to create a DRM free Transformers comic collection to benefit the Hasbro Children's Fund. Available from now until around October 29, you can get nearly the entire current run of IDW's Transformers comics up to the Revolution storyarc that just started. Per usual, the bundle is segmented but at a value of $405 so you can't beat the deal with most of the proceeds going to charity so you should really consider donating over the $15 minimum for the full bundle. These purchases are not tied into Comixology or other online retailers.
If ordering I recommend creating a Humble Bundle account first and then log in before donating. That way it automatically ties your purchase to your account to re-download if need to in the future. After donating you will receive an email that directs you to the site to download the books in your preferred format. If interested in the .cbz format of the books, the readers I use is ComicGlass for iPad/iPhone, Cover for Windows 10 and Perfect Viewer for Android (but add your own suggestions in the commments). If go with epub format, Play Books from Google will probably more that meet your needs in most cases and includes syncing across devices.
Full details are at Humble Bundle.