I own an Impact Mk2. It has a .25 700mm slug liner. It's a decent gun, but IMHO lacks simple ergonomics. It's bulky, and a bit awkward. It's a good bench gun, yes, and very accurate when tuned correctly.
Is it great to shoot offhand?? Not really. It isn't balanced well, and just feels like a large, bulky gun... Kind of defeats the purpose of the bullpup. Try offhand shooting a Taipan Vet Shorty, or Edgun R5M/Lelya. These are the offhand rifles which absolutely shine... and equally accurate.
I'll probably catch hell for saying this, but the Impact is really over-hyped. This is my opinion, from having owned all the above... and as we know, opinions are like a$$holes, everybody has one.