1. Tri tips and sirloin steak tips are the pointy ends of rump and sirloin respectively. They are ideal for kebabs because they have great beef flavour, hold up well in a cube shape, are juicy cuts and are more economical than expensive steak cuts that I reserve for cooking as steaks.
In Australia, Tri Tips is part of the Curious Cuts economical range sold at Harris Farms - described as the best part of the rump, and I agree!
Sirloin steak tips are not sold in Australia, except by special order at butchers. The sirloin tips are kept attached for roasts. They are more common in the States - sometimes labelled as "flap meat".
Alternative cuts: Use any other quick grilling cut of beef EXCEPT those that need to be sliced thinly against the grain to be tender to the bite (eg skirt, flank). Rump, sirloin/porterhouse/New York strip (same thing), economical fillets etc. Buy it in a block so you can cut big cubes.
2. Don't worry, it won't taste Asiany. Soy sauce is a brilliant brine to tenderise meat. Use all purpose or light soy sauce. Do not use dark or sweet soy sauce.
3. If using bamboo skewers and cooking on the grill, soak in water for 30 minutes before using and use 2 skewers per kebab, side by side about 1cm apart, so the meat doesn't spin when you turn them (which is what happens if you use 1 skewer).
4. Pink Steak Sauce pictured in top photo is kind of like Yum Yum Sauce which is the sauce served at Japanese steakhouses in the States. The Kabobs are so juicy, it really isn't required, but I know some people are big fans of Sauce! I used: 1/3 cup mayo, about 1 tbsp ketchup, dash of tabasco (or hot sauce) to taste, 2 - 3 tbsp milk (or water), 1/2 garlic clove minced, pinch of sugar. Mix, thin with milk as desired, and set aside for 10 minutes.
5. Nutrition per skewer.