Having just picked this up today and made a brief scan of it, I can honestly say that I'm a bit disappointed in the battlesuit stats. I can understand FFG wanted to provide something very cool without breaking the balance of power, but I fear they went too far trying to fit them into the existing balance to accurately reflect their capabilities.
The main issue is that they are treated as armour, and there's enough high-pen weaponry floating around (not to mention stuff that can outfight ignore it) that the squishy little pilot doesn't stand a chance in any sort of really heavy fire-fight. Comparing them to the battlesuit profiles from Deathwatch, the ones in this book are just utterly outclassed. Sure, Deathwatch is a much higher power level than Rogue Trader might be, but there's certainly a few things they could have taken from their previous examples of battlesuits to make the ones in their latest PDF more appealing.
First off, unnatural characteristics for Strength and Toughness. Admittedly, the way UCs act in RT and DW make balancing them out a little trickier than, say, Black Crusade and Only War, as the bonuses can jump pretty quickly if you stuff a pilot into them with high base stats. Given the average Tau pilot isn't likely to have prioritised these however, it would certainly give them a little boost that would help a lot, and could easily be justified as part of the internal systems of the suit.
Another option is to treat them more like a half-and-half between armour and vehicles, a little like they did for Dreadnaughts. The player's statline still dictates most of the relevant abilities, with a few like Strength being boosted, but the armour has its own structural integrity rather than coming directly off the pilots wounds. There's already a table provided for critical effects on the suit, so it wouldn't be a difficult thing to amend, and there's the option for increasing the suits tactical/cruising speed beyond just the pilots Agility + size modifiers if you feel their ground speed was a little on the slow side. Doing that would alleviate much of the need for having Unnatural Toughness, but would still keep the battlesuit relevant in heavier combats.
There's not a lot I can add to the weapon loadout stuff since it's already been pretty heavily covered.
To be honest, the suits aren't terribly set-up, and with a little light tweaking I could see myself putting them in a game of Rogue Trader or possible Black Crusade/Only War (where adding Unnatural Characteristics would be a lot easier to do in terms of keeping power balance). I just think it's a shame FFG felt they had to low-ball them so hard.