I am not too keen on the idea of the smoke either.
But after reading a review from a 335d user in UK that could not see any big difference in smoke and after speaking to my tune guy who told me he can control most of that in the mapping I not that scared.
Actually he told me, my tune only gives aprox 7% more fuel than OEM. And that has given a powergain of aprox 35hp and aprox 100nm.
And yes, some tuners do promise a lot of powergain with small adjustments or changes. I have heard of tuners here in denmark saying they can get up to +60hp only by remap the ECU. That I think is doubtfull.
'06 E91 330dA Sparkling Graphite|19" AvantGarde M359 Satin Black|335i brakes|Bilstein B16 IRC|Powerflex|GroundControl|Wagner|Ecotune|Turbo Dynamics|Zimmermann