It's rough around the edges, which is understandable as an early beta version, but it is extremely useful to have. Invaluable for showing what has been backed up and when by Time Machine, and for identifying files that have pushed up the size of those back ups.
There are a few stalls and pauses as it calculates the sizes of back-ups which can give the sense of a frozen app (especially immediately after launch) but, when left long enough, it eventually revives itself. Therefore, it could do with a more visual representation of what it is doing other than a simplistic spinning dial and "Please Wait".
UI and preferences need work to make the look and feel better, and improve the feature set (e.g. the option to use MB in place of MiB etc. - I find it harder to register the 'iB' nomenclature.