AVC = Pre-Retirement Product
ARF = Post-Retirement Product
Two distinct contracts so you have to select the fund on the 'new' contract.
You could also vest the PRSA (stay in same products minus the tax-free cash you take) but it's likely that you you might get a better AMC on an ARF. It depends.
All funds on ZL AVC are available on ZL ARF.
If you're in (say) International Equity Fund (identical Other Ongoing Charges cost on both contracts) on AVC and want same fund on ARF then that's fine. There is no spread. You'd have to go out of your way to buy a pension product with a bid/offer spread on it. You should be able to buy, without difficulty, an ARF with 100% allocation. You might have early exits (ony applicable to transfers, not withdrawals) on the ARF (depending on where you buy it).
If it's an internal transaction, you mature the AVC today and sell at the bid price at close of business tomorrow. You buy the ARF units at bid price on same day. No 'loss'.
Gerard