Sorry to be a downer here, but ultimately the device will likely do more harm than good. As you mention, the effect often wears off quickly. Once it provides fluency once, it's hard to not yearn for it again and again, making it difficult to "just use it when you need to". Although it takes more effort on your part and more time, if there's a way speech therapy could be paid for, finding a stuttering specialist who does NOT focus on directly increasing fluency would be a good long-term option. This approach can lead to increased confidence and spontaneity when speaking as well as decreased fear of stuttering - and sometimes as a byproduct of this, stuttering naturally decreases. Happy to share more if it would be helpful.