technically it isnt a buff its more of a balancer, it alters your stats when u enter seng.
there is a huge difference it becomes way more noticeable the more you level and the better gears u get though. it makes some stats higher and some stats lower to make pvp more balanced. well so it says it dosent do a very good job at balancing at all in my opinion.
for example a priest would gain a lot more magic attack but loose physical attack. while the buff is active. the buff also changes your hp and mp makes them higher, last time i participated in a seng i went from like 2k m-atk to 12k m-atk so yea theirs a great difference that's just an example tho.
i dont know how they work it out but people inside seng could kill my priest easily yet outside seng in places such as kaymo that same person wouldn't stand a chance against me. thats how much difference it makes. it strengthens your classes attributes