I have used both the Arrowmaster and Bowmate. My brother owns an Arrowmaster and I own a Bowmate. Both are slightly different executions of the same concept, both work excellent. The weight difference is not stark, a handful of ounces. The primary advantage of the Bowmate is that it is a rigid tube, so additional protection of arrows is possible, and it is also ambidextrous, whereas with the Arrowmaster you must choose RH or LH model. The Arrowmaster is a semi rigid design with an internal frame. It is perhaps a little more roomy. The broadhead foam in the AM is also more durable, howver in the Bowmate it is just a piece of pool noodle, so for 1.99 at Walmart you can purchase a lifetime supply
I would gladly own either, and chose the Bowmate because I liked the pocket on the lower end and the ambidextrous option. Both excellent. I would go with whichever one strikes your fancy the most.