Endowments are now quoted at a rate of 6% or even lower depending on the fund selection. It used to be 8% but this was about fews years ago to be honest I thought it was five years since it changed, time flies!! What is effectively means is that the fund needs to grow at the quoted % p.a. to provide sufficient at the end of the term to repay your mortgage. The fund/s selection is therefore very important. For example, if you were invested into cash you probably could not hope for more than 3% p.a. but if you were is say property, most of these have been producing an average of 15 to 18% over the past few years, many even more. The requote that they are doing is probably based on 6% growth so a higher premium would be deemed anyway.
As you said you were always worried about such a mortgage so it probably was not for you from the outset and a good advisor should have identified this.
I have an endowment mortgage effected two years ago, just got my statement and the accumulated fund is just over €12k. If I had gone down the annuity route I would have only repaid just under €8k so I am quids in at the moment, obviously I will keep an eye on my funds. They are not for everyone, particularly where you are not made aware how they work from the outset, and what fund the person is invested into, personally I would not have anything else however I know quite a bit about investment so I have a little bit of an advantage.
Presently €258 per month at 8% would give you aproximately €244k in 30 years based on savings only (no life cover) the same premium would give you €178k in 30 years based on 6%. This is only a general guide, the actual amount is dependant on the actual contract.