Is the Nature publishing group's "Scientific Reports" journal well regarded? The Journal "Scientific Reports", published by the Nature publishing group, is gaining popularity with time (impact factor now around 5.2). It highlights its editorial policy as one that is focused on scientific rigour and validity, rather than perceived impact.

My question is: 


How well regarded is "Scientific Reports" in the academic community compared to other more-traditional ones, especially in the physical sciences and engineering? 
Also, does the fact that it imposes article processing charges and publishes only open-access articles reduce from its perceived rank as a journal? 
Is its high impact factor a result of these factors, or is it actually due to high quality articles published in it? 
Many researchers know that some well-regarded specialist journals might have relatively low impact factor, but their reputation is still top-ranked. Say, for example, that I have a paper in physics or engineering, and I could either publish it in a specialised Physical Review or IEEE journal versus Scientific Reports, which one would be more well-regarded (assuming the first two have less impact factor than Scientific Reports)?
My take: any journal that considers rigour and validity only, and not perceived impact, will be less well regarded than an equivalent journal that has a good reputation for rigour and validity and also considers impact. 

On the plus side:


Page charges are normal for open access, and open access is a positive, so I don't think there's a problem there. 
As a Nature journal, Scientific Reports inherits a little of the "glow" of Nature, which will lift its reputation relative to other journals that don't consider impact (e.g. Helyion and PLoS). 
Nature journals employ full-time professional editors, which means that people submitting to Scientific Reports can also expect fast, professional review and editing. This help's the journal's reputation, too.


An impact factor of 5 is very high in many fields, but nothing to crow about in other fields. So I would expect this journal to attract higher quality papers from those fields in which 5 is considered a high impact factor, and lower quality articles from fields that typically have high impact factors.