There is a risk the new scheme may underperform
All eggs in one basket from a provider/fund point of view.
Your old pension is now locked into your current employment. You must abide by these scheme rules with regard to any potential early access.
Different rules with regard to fund passing to your estate on death. As an active member up to 4 times, your salary and the value of your contributions can be paid out as a lump sum. Anything over an annuity must be purchased.