Terrier personalities are attractive because they have more spark than Gundogs which were developed to wait for an order & then react.  Terriers do not take orders, but know their job and do it. They don't wait for orders either. Glens, by their nature, may appear more submissive than some other terriers but they WILL take advantage of wishy-washy non alpha owners.

It's certainly less relaxing than having a breed with an inbuilt heritage “to please” but way more interesting. Is this what you want and can you be self-assured, consistent and firm as well as fair, calm and kind?