In short -
A BIG YES.
Simply using the device is the world's easiest and most efficient way to maintain size gains.
It doesn't matter if you are looking to preserve gains from Bathmate or size gains you have made from manual PE exercises such as jelqing or stretching - Bathmate can help you keep the majority of your progress.
It's easy to do too.
Just use your pump 2-3 times a week for 12-15 minutes.
That will help you maintain 90% of any PE gains you have made.
That is exactly how I've maintained size.
If you really do not have the time or motivation to do other PE exercises anymore, just the Bathmate will do enough to preserve (in some cases even increase) your girth gains.
Ideally, however, you should combine Bathmate, jelqing and stretching (manual PE and/or extender) in order to preserve and extend your gains. You could rather cut back on the session duration than to cut one exercise from your routine altogether.
Using the Bathmate 2 or 3 times a week for 12+ minutes will help you maintain the vast majority of your size gains, regardless of how you gained the size.
It is the ultimate tool for maintenance, that's exactly what I use it for these days.
(other than for inflated girth in the bedroom)