Thanks for this OMG client with Coin Control.

But I wonder how much can I rely on the tx size/fee estimation in Coin Control?
I just noticed that tx size estimated is 300 bytes less than actual tx size in some cases.
Maybe that's a minor bug?

The underestimation in tx size occurs when multisignature address is involved.
This tx
https://blockchain.info/tx/d84613726465c27ce641bd20a4385dfada887effee99d77b01548e13403066d2
contains 5 inputs and 2 outputs.
The address starting with 33 is a 3-of-3 multisignature address.
The actual size is 1264 bytes, but in Coin Control it is reported as 946 bytes.

Coin Control does not check the address type, I guess.
Multisig address is larger than normal address, and ignoring address type leads to this underestimation in tx size.

Hope this could be fixed soon, and we can expect a reliable fee estimation.