Not having used the BDS product I cannot comment. However, I do have the IRO 3.5" F>R kit with the double shear track bar and it is very nice. I love the build quality and how fast they respond to any and all questions via email and telephone.
I live in the middle east and they had the kit, including new axle shafts and axle shaft sleeves shipped to me within 4 days. 4 DAYS!!! Any other company I have ordered from has not got my stuff here in less than 2 weeks and then some of the stuff was wrong, or was sent to the wrong address.
I say go with teh IRO kit as it is great value for money, amazing customer service, fast shipping times, best shpping rates I have encountered, excellent quality and just altogether nice people, but again, I aint used BDS for anything so can't honestly comment on that side.
Good luck with whatever you choose.
FWIW, I have a rear track bar drop bracket and have not had an issue when wheeling. If installed correctly (using lock washers instead of normal washers) you should be fine, but I wheel on sand and that makes a lot of difference.