Is the Nature publishing group's "Scientific Reports" journal well regarded?
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.