It largely depends on what other servants and CEs you have access to. If you use him like most other berserkers, hes not going to match their damage output. On the other hand, if you have ways to give him guts and provide plenty of stars he’s an absolute monster. His NP hits extremely hard at low health even at NP1, and his crit buff is comparable to or even better than JAlter’s as long as it’s used around half health or lower.
Servants like Irisviel, Summer Umu, and even Paracelsus work wonders for keeping him around to try and take advantage of his gimmick, but even with guts he still might explode before pulling off his amazing damage potential if the enemy attacks line up wrong. I haven’t played around with it yet but predictive evasion on the arctic uniform should be a good thing for giving him some extra padding, and his bond CE starts him off with guts and a NP damage buff.
I think he’s a fun servant to use, but trying to force his gimmick to work without the right team comp would be pretty difficult. Even with everything he needs, don’t expect him to stick around for more than 1-3 turns once guts procs and he gets his NP and/or crits off.