I have 420K XP and 14 Captain points on my Blyskawica. I also recently acquired the Kiev. The two ships have many similarities and can perform the same role. The Blysk is more rounded in its abilities, however, than the Kiev, with the Blysk easily being a better ship to have in the stable. The most notable differences of the two, as has been mentioned already, HP, invisi-firing and torpedo range. I survive many more battles in the Blysk (45% vs 20%) than the Kiev, particularly when I'm patient and remain in a crowd or 13K from the nearest enemy. AFT is an absolute must for the Polish Lightning, as it easily doubles the damage the ship can do in a game from the safety of the rear area.
Blykawica's greatest weakness is her dinky 120mm guns. They merely tap, tap, tap the enemy ships, particularly at range. Firing HP I average only 200-250 damage per hit. Of course about 3% of these turn into fires (but it's nowhere close to the advertised 8%) which cause additional damage. Any upgrade/skill that turns up the volume of the pitter-patter guns is worth getting. The slow torps with their small invisi-fire window make the fish useless majority of matches, as well. This ship is capable in the right, trained hands, but it's a long way from being OP. Expect many, many fun-filled hours getting the captain skills up and running, along with optimizing both the ship and your skills driving her. It's not a vessel that one tires of quickly, as it's profoundly easy to learn but hard to master.
Finally, one of the most challenging aspects of the Blysk is playing it in such a way that won't upset your team members. My teams always expect me to spot (which leads to discovery, incoming fire, evasive action, smoke, and the losing of 1/2 HP), whereas, the Blys much prefers to hover in the back, sniping at range, and setting fires. I've finished many games as the point leader or close to it, but in the process have been called a host of vulgarities by sunken teammate trolls for not exposing enemy targets for them to shoot at.
I'm working toward CE now which should allow for shooting at closer range, increasing accuracy and hitting power, as well as, giving a little more wiggle room for launching those flaccid torpedoes.