There is absolutely nothing wrong with a street tune from a competent tuner. There is no real need for a dyno when tuning a NA Z. That being said, OP's tuner sounds inexperienced to say the least. I would feel much more comfortable doing a remote tune with Seb at Specialty Z.
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2011 370Z 6MT Sport Gun Metallic | ARC | CJM | Ecutek | FI | Fujimura | R2C | SPL | Stillen | TWM | Z1 | ZSpeed | |