Just get Uson, more efficient expenditure of resources. Useful in a far wider range of activities (unless all you do is fight fodder weak enough for physical magic to be applicable a majority of the time).
Going from Uson -> Mimesis
Base D: 135 -> 128 (-5 ~ -7 for DEX, -7 ~ -9 for STR)
Delay: 231 -> 236 (+5, negligible both ways)
Accuracy: -12 ~ -13 ACC for DEX; +3 ~ +4 ACC for STR
Attack: +7 ~ +8 ATK for DEX; -8 ~ -9 ATK for STR
Req Base Damage: +1 ~ +3 for DEX, +2 ~ +/-0 for STR
CDC Base Damage: -3 ~ -5 for DEX, -1 ~ -2 for STR
Very minor base damage increase for Req if we consider DEX Uson, even more minor if considering STR Uson (especially when attack is taken into account). Even more minor, possibly even inferior (though unlikely), when you consider that both the main and offhand hits will have lower base sword damage due to wearing Mimesis in offhand compared to mainhanding a Uson and offhanding a Bura; i.e., 5 hits, before multihit, are affected by Uson's superior base damage compared to Bura; all six hits, before multihit, are affected by Mimesis' higher WSC, but also by the combined lower sword base damage of Bura and Mimesis.
Mimesis is flat out worse for CDC. Sanguine Blade is Sanguine Blade. Shouldn't be using it all that often, and it's normally sufficient for its purpose when you do need to use it regardless of the extra INT, MND, and STR on Mimesis.
This leave's Mimesis' main advantage as being better than either Uson for physical magic, this varies depending on spell; some will have more gained from Mimesis while others will gain very little compared to a STR or DEX Uson. Physical magic is almost entirely ineffective, however, so this advantage is limited. STR or DEX Uson (DEX being best to make first) are better investments as long as you don't only use BLU for fighting things that are EM or lower (at which point I'm not even sure I'd bother spending money on either sword, especially if you already have Anahera saber and Buramenk'ah, but that's your call).
For off and Main hands:
Capped ACC on targets between VT and IT+++++++++++~:
Uson STR > Buramenk'ah* > Mimesis** > Anahera Saber > Other things
Uncapped ACC on targets between VT and IT+++++++++~:
Uson DEX > Buramenk'ah* > Mimesis** > Anahera Saber > Other things
Targets between TW and T:
Mimesis** > Uson STR > Uson DEX > Buramenk'ah* > Anahera Saber > Other things
*Always a better offhand than a second Uson or Uson/Mimesis unless accuracy is so severely impaired that you make great use of the ACC from a second DEX Uson.
**Offhand with Bura or something. Mainhanding would be a DPS loss. This is assuming the use of physical spells on applicable targets, which creates a very small gap between Uson and Mimesis.