IMO, the "features" to look for are:
1) Strength of the material. You'll want studs that are of a grade equivalent to OEM fastener. The BMW wheel bolts are grade 10.9 I believe. You don't want a softer material or even a higher grade, because the ability for fastener to clamp the wheel onto the hub is highly dependent on the stretchability of the material AND the durability of the fastener is dependent on the strength. Therefore a very narrow grade of steel needs to be used, or at least the equivalent of that.
2) To prevent galvanic reaction between the nut and the stud, it is best to have anodized or powder coated studs. A bare finish CAN result in seized nut to the stud.
3) Length of the studs will determine what size spacers you can run, but if the spacers are larger than 15mm you shouldn't use them on studs anyway. 15mm or larger spacers SHOULD BE BOLTED TO THE HUB.
There are a couple of additional features that will be beneficial but not always necessary. Allen key ends or hex ends on the studs will make installation and removal (and you WILL remove them. All fasteners, even BMW OEM lug bolts, should be replaced after x numbers of use) much easier. Also, bulleted ends will make installing the nut a lot easier and decrease the chances of cross-threading the fastener if you use an impact tool.
This is what I use:
http://www.racingbrake.com/RB_Wheel_...t_p/bmw-80.htm
I tried to set up a group buy deal here a long time ago, don't know if the deal is still valid...But if you search on their website there's some references to it.