That is poor, rounding on Brydon's latest impressions (6)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

I E (that is) + ILL (poor) reversed or ’rounded’ after or ‘on’ N (last or ‘latest’ letter of Brydon) – we would never have heard of niello/nielli if it had not appeared so often in crosswords