personally i have never liked using or having the kritz used on me; having 100% critical hits is kinda worthless if there is always that one pyro, that one spy, or that one anything that slips by and kills you
basically, you always have to be aware of your surroundings as any class, but if you are a medic with ubercharge ready to be deployed its more risky; with the medigun if you get hurt you can just activate uber and uber someone to help take care of the enemy in the meantime or use the uber to go to get health packs - with the kritzkrieg its kinda you're 100% vulnerable 100% of the time; it doesn't give YOU crits when deployed so its useless if you need to defend yourself while escaping
basically, you always have to be aware of your surroundings as any class, but if you are a medic with ubercharge ready to be deployed its more risky; with the medigun if you get hurt you can just activate uber and uber someone to help take care of the enemy in the meantime or use the uber to go to get health packs - with the kritzkrieg its kinda you're 100% vulnerable 100% of the time; it doesn't give YOU crits when deployed so its useless if you need to defend yourself while escaping