Armstrong moved to Saints last season from Celtic.
He said: "It's been an interesting one. Obviously changing teams is a big thing, it takes time to adapt and go into a different league, which is in a lot of ways very different.
"There has been a change of manager too so it's been up and down, but what I've found playing football over these past years is that football is always up and down and you should never be too high or too low.
"I certainly think I have learned a few things, experiencing different types of games, more physical games, sometimes faster games.
"You have the privilege at Celtic to dominate games and we were winning more than we were losing. Sometimes down the road that's not the case.
"Trying to learn from those experiences is something I am quite enjoying as a football player."
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