Yesterday I emailed what I thought was a viable tactic to Marshall Learoth about Sword Brethren with the Infiltrate skill in a Razorback with a Twin-Linked Lascannon. If you're sharp you can immediately spot the mistake I made. Otherwise, or for a more in depth look at both the email and Learoth's comments, you can read his blog post here: http://www.implausiblenature.net/1/post/2011/03/email-sword-brethren-infiltrating-razorbacks.html
So, I'm still looking for a worthy use for Sword Brethren that makes them worth their points. This is not very easy since they have both cheaper, scoring Crusader Squads and hard, deadly Terminators to compete with.
Currently I'm examining using them as something of an assassin group by putting them in a drop pod with Bolters an assault weapon and Counter Charge. Drop them behind enemy lines and get a rapid fire off along with being a dangerous unit to charge. But I still have the problem of making them a better option than transporting Terminators in who have a bunch of power weapons and can even fire heavy weapons their first round. But they are a better option than using Initiates for this with their Counter Charge Skill.
Well, that's all I have for now. I'll be sure to give them a full examination sometime soon though. I hope to start a series so that I make sure I look at units completely.