My account may seem fairly new here, but I've actually been using this application way before I created said account, like about a year ago. As someone who's played SCGMD4 since the year it was released (2012), I am ecstatic to see that I can finally be able to make my own maps in the style of the iconic series, something that I've been fantasizing about for years.
The way the program looks is decent, and the editor timeline feels like an actual guitar skin in SCGMD4, which has me feeling extremely nostalgic.
However, there are some things I'd like to mention, regarding the editor. There seems to be no beat snap lines for the BPM and no way to zoom the timeline in and out. Making sliding keys be much longer than the window (similar to the end of most songs in the SCGMD series) is pretty hard to do, as it seems that you cannot unpause/pause the timeline using a key and without having to manually click the playback button.
Other than that, as someone who likes making rhythm game maps, I really like it a lot! It always satisfies me when there's an unofficial editor of a rhythm game that doesn't have an official one.