I've been looking over the advanced specialities, and noted their usually very high xp cost prereqs, and the often redundant and very overpriced talents and skills in their advance tables - and I've asked myself, "Is it worth it, to purchase any of them? (pure RP-purposes not included)".
For example, the Black Shield, its advance table could be considered a "chapter advance table", but it more or less contains what you will find in the rank 1 space marine general advance table - a bunch of redundancy skills and talents which any space marine start with. Sure, it's free, and you get some abilities, but the table makes me wonder.
Another example, and the one making me ask the above question, Deathwatch Champion has an entry cost of 4000 xp. It could be seen (especially from a RP perspective) like more or less a "natural choice" for an Assault Marine (which was what I was basing taking the specialisation with), but more or less every talent on the champion's table you can find on the AM's tables for half, third or even a fourth of the xp price. Sure, you get access to some higher ranked talents a little earlier, but they often cost three or four times as much. The earlier access to Dodge+10 and +20 are nice, I'll admit, and so are the Signature Wargear: Hero talents, as well as the Xenos Bane ability. Other than that, it just seems overpriced and redundant. A Tac wanting to focus on melee might would be content with those prices, not having access to them at all, but he'd not be able to get many before reaching rank 8, considering how much they all cost.
4000 xp for the specialisation with Xenos Bane included in the price. 800 for the cheaper skills, 1000 a pop for the sig wargear talents and the rest you can get much cheaper, although perhaps a little later (but by spending xp on the things you want, you'll probably reach a higher rank anyway) - most talents you've already gotten, or can get soon without dumping 2000 xp on something. Just doesn't seem "worth it". But hey, maybe I'm just too concerned with building myself a well-rounded character while affording all the talents I'd like to get and have fun with?
I've not looked too much on the other specialities, but I think it's pretty much the same there. Forbidden lore: The Black Library for 800 xp on the Epistolary's table, when it costs 400 xp one rank earlier on the Deathwatch table? Yeah...