I would like some comments on this build.

Master, Battle standard on Dark Pegasus
Repeater Crossbow, Lance, Heavy & shield, Sea Dragon Cloak
Cloak of Twilight

1+ Armor save
3+ Ward save against W's caused by shooting A's & magic.
1st round CC Killing blow & Multi W's (D3) (at S6 with Lance)
Can shoot when not engaged in CC

Good build or not?

Pretty much a staple build of many a list.
Absolutely nothing wrong with it.

I'd ditch the xbow. You can't do alot with it. It's not fast cav and so there is no marching and shooting. I don't particularly like combining the CoT with a BSB because I find it too tempting to take the master away from the main attack wave to pick off trebuchets or iron blasters or... . If you have the patience to keep him close then these two items will work well. This combo is not for me anymore.

My favorite build is to run full mundane with talisman of preservation and charmed shield. 4+ ward save, 1+ armor and usually ignore first cannon shot goes a long way. This also frees up the CoT to go on another peg lord/master. If you're doing it right, the cannons only GET one shot

Charmed shield can be picked with a single dwarf crossbow though

Cloak of Twilight is the best ranged defensive item by a long way. Its offense is better spent on a dreadlord, sure, but in my opinion the BSB is more important (LD8-9 with reroll far beats Ld10 without!), so theres nothing wrong with giving the BSB the cloak.

I'd say...why not both! My BSB runs the Charmed Shield 4++ and another master takes the Cloak into the enemy. I've found through playing that I was very uncertain about committing a cloak BSB into any combat, because if things go poorly and he breaks, he's just dead. With two pegmasters flying around, the cloak can run around and pick off high value targets and assassinate characters, while my BSB can fly where he's needed the most, avoid dangerous enemies, and opportunistically pick off weakened enemies/chaff as needed. Plus, the added target saturation means that at least one of them will still be limping around near the end of the game too