This is a good calendar and reminders application. Apparently, creating a calendar and reminders app is very difficult. There are a bunch of them and most are bad and/or dont work with all the iDevices and/or have some other bad oddity.
Not all features work in all screens. Example: Drag and Drop only works with the "Interface" of Tabs in the Month calendar view. Then only by selecting the day and from the day section (upper right), select the event or reminder, by holding it and then draging it to a different day. This means you cannot drag and drop to change the time, nor can you drag and drop from any other view in any other interface.
Be prepared to do a lot of editing to get the esthetics to your liking. The developer(s) have made a huge error in providing many cosmetic options for this app. By providing the options it is easy for a user to get lost in the verbage. The option labels are not clear ("Back Color" & "Cal Back Color", I could not figure out which one changes what.) and not all possible options are available (no text color option). It would be a big help if the developer would hire a designer. Then remove the cosmetic options and leave a small number of themes. Also, they should remove the "Interface" option and just pick one, that would make testing all the themes easier. As is, not all screens work with all themes/options.
My guess is the developer is trying to be everything to everyone with this app. Frankly, the end result works, but it is a mess.