I too like my BLI ATSF 3751. But I do note the following discrepancies on my model:
1. The locomotive model has three cross compound air compressors - one under the cab and two on the pilot beam. On the prototype, when the Elesco feedwater heater was exchanged for the Worthington type, the pump was put on the pilot beam where one of the air pumps was located (engineer's side of the loco) and the air pump relocated to under the cab on the fireman's side. So the model should only have two air pumps. The model has the feedwater pump on the pilot beam but it is inbetween the two air pumps.
2. The stack extension (which I installed) does not appear to be the same as the extension that was used on the 3751 when it was in regular service, although it does appear to be one of the types used by the Santa Fe on other locomotives.
3. The tender capacity lettering on the back of the tender is incorrect (I replaced it with decals). Interestingly, the preproduction photo of the engine on the BLI website has the correct lettering. I find the engine will not take an 18" radius as indicated on the BLI website but runs very well on 22" radius. This may be because all drivers are flanged and the 80" drivers make for a long wheelbase. My BLI M1b takes the 18" radius very well, but, as with the prototype, has the two middle drivers, on both sides, without flanges.
4. The sound system only provides three chuffs per driver revolution instead of the prototypical four chuffs. This is not noticeable unless you look for it, but once you find it, it is disturbing. I spoke with BLI about it but they said new software was required to correct the problem and they did not know if that would be done. A similar problem with their PRR J1 was corrected with a new chip using M1 software.
The engine is otherwise detailed nicely and runs and sounds very well. The off color paint job, under my lighting, looks like faded black and doesn't bother me.