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

'impressions' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'that is poor rounding on brydon's latest' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'poor' becomes 'ill' (I've seen this in another clue).
'rounding' shows that the letters should be reversed in order (I've seen 'round' mean this).
'on' means one lot of letters go next to another.
'latest' suggests the final letters.
The last letter of 'brydon' is 'n'.
'ill' in reverse letter order is 'lli'.
'ie'+'lli'='ielli'
'ielli' after 'n' is 'NIELLI'.

Can you help me to learn more?