Experts by no means recommend using ETH on merger day.

The experts recommend ceasing all the transactions to zero. The most commonly anticipated issue is that the ETH price will most certainly start to vary on different DeFi exchanges.
Another serious problem that may take place is reorg. What it means is that the ordering of the blocks on the chain will change which may cause a lot of lag as transactions get stuck and returned to the mempool.

On top of that you should also worry about transaction delays between POW and POS chains which will be increasingly higher on the day of the Merge. By the way that is exactly what will cause the above mentioned price differences on different DeFi exchanges.

To round things up, the Merge is going to be huge, and even with all the risks on the table we still have an unprecedented event that will mark the beginning of a new era for Ethereum introducing faster, cheaper, more flexible and at the same time more powerful smart contracts than we have ever seen.