Packt Reviews 

Predatory subscription service: I had subscribed to 7-day trial. They did not send the email confirming the trial. Furthermore, Packt did not send any notification before or after the payment was taken. I happen to scan through my card statements and saw I was charged for May and June without any emails. When I contacted support, they claim my card company or bank should send me email, ridiculous! Finally, after cancellation, now the email arrives reminding that your trial is about to end, please renew - Ha! not even in your dreams! Except few books on packt collection, this is worst thing one can subscribe or buy from.
Oreilly is the only best service, don't fall for this aweful service.

Bought a book from them that had "unlimited" access. After a short time when I tried to download the book I got an error "invalid link." When I contacted them I got no response.

Content is generally of a poor quality, but there's lots of it.

Billing changed without notification to be on auto-renew for one year - with no response back from customer services when asked to explain this.
Billing is generally an issue - it's always been unclear (they state one thing, and really something else is in effect - they then say the site is buggy and what you see is not a rue reflection of the account) and the functionality of the website is buggy.

You're better off purchasing a membership with O'Reilly for tech books or subscribing to a service like pluralsight.com or codeacademy.com or datacamp.com or dataquest.io

Avoid this service - it's really not worth it.