Aluminum crampons are great where you know you'll only be on snow, no mixed rock and minimal ice. One caveat though is that they dull faster than steel and have been known to crack in super cold weather. Steel is heavier, but more durable, dulls slower and better on icy areas in my experience. I have climbed Whitney in aluminum and yes they're lighter for sure. I removed them once I hit rocks and put them on again when it was pure snow, which is a pain though I wanted to preserve the points.
So, as far as which crampons to buy, it will somewhat depend on you and your future plans other than Mount Whitney. If you plan to keep using them on more mountains, maybe more technical mountains or peaks that have some rock mixed in, a steel pair is probably a better investment than aluminum if you are only getting one pair. The BD Contact Straps are good and I've used them on Whitney, though I like Grivel models better. If you do buy a mountaineering boot with a rear welt for crampons, get a hybrid strapon model with a rear clip which will be more secure all things equal, like a G12. The G12 is more aggressive than the BD C/S models but you feel better on steep slopes in them.
When attempting a lightweight climb, I have tried with some success to use strapon crampons with lowcut trailrunners, but the fit wasn't great and didn't give me comfort on icy areas due to that. They were fine in the flatter areas, but my shoe was too soft for them to tighten tight enough to give me comfort on any of the sections with more consequence of slipping. On those climbs though I knew ahead of time there was on a couple spots I needed them and there wasn't a lot or any postholing either.
Trail runners are great on Whitney when there is no snow or just a little snow on flatter areas. I use them on most summer/fall hikes/climbs until there is more meaningful snow, then the mountaineering boots come out. If snow is deeper than 8-10", I'll add on gaiters. If its a more technical route and dry, I'll opt for an approach shoe that can be hiked in.
One other point with trailrunners vs. boots is warmth/water repellency while hiking all day in snow. Boots are a clear winner for those with a tendency to get colder feet or where you're postholing a while, boots will give you an added few inches over trail runners to keep the snow out and help better to keep your feet dry/warmer.
You didn't ask about an axe, but you should prepare to have that as well and as you practice with your crampons get some instruction on proper ice axe use, self belays, self arrest, etc...
Good luck!
