I'm really glad to see Grass Sticks using adjustable straps now. That was the one thing I didn't like about the product when I met those guys at Copper last year. Seems like a really high quality pole and I think bamboo will outlast aluminum most of the time. I'll have to pick up a pair for my kid.
I never thought I'd use anything other than the cheapest aluminum poles I could find, but about 8 years ago, my wife bought me some K2 composite poles for Christmas and I have to say I love them. To this day they are still arrow-straight and have no nicks or scrapes.
I bought a separate pair of poles for slalom because I didn't want to keep swapping the guards on and off, and I bought the LEKI Trigger S. I found a fantastic discount on them and you will need to as well to get under the desired price point, but they are awesome. Instead of a traditional strap, the have a little eyelet thing that connects to the pole grip by a spring-loaded mechanism, allowing you to have the strap firmly connected to your glove, but have the freedom to easily disconnect from the pole between runs. The pole itself is the highest quality aluminum pole I have ever encountered.
As far as length, I've seen it stated pretty emphatically that you must measure using the 90 degree elbow test while in your ski boots and clicked into your skis to measure for the stand height you'll be using on the hill and this is the exact correct measurement for everyone and if you deviate from this you are doing it wrong and it will be impossible to ski correctly. Personally I think that's rubbish, but it's subject to debate I suppose. I think the elbow test with street shoes on gets you into the ballpark and individual preference can vary by a few CM, so it may be worth to hit up a rental shop early season and try a couple different lengths to see what works for you, length-wise. Personally I've never bothered to dial it in that precisely (but then I'm not the best skier.)