Poems is offering it because of the tie-up with Moneyowl/Temasek Trust. While in the short-term, I'm pretty certain that Temasek Trust is committed to this, there is always a risk that TT will discontinue their partnership.... nobody knows what will happen in 10, 20 years.
Stocks seem relatively easy to change custodian, but unit trust, if Amundi doesn't pay the unit trust custodian any fees, it may not be so easy to move your holdings, though worst case just move back to Endowus and pay their fee (in which case it becomes worse than VWRA).