Picture quality is same on HD and HD DVR. It is good, undoubtedly. DVR is manufactured by Pace brand which one of the top set top box maker. With HD DVR, you can remote record via mobile too.
Install Tata Sky app - available for both android and ios.
Login with your Tata Sky sub id or RMN.
Go to My Box tab inside the app and select program you want to record. Note: STB needs to be on ON mode while you make request and program arrival time.
You can also connect STB to same wifi network as your phone, pair the STB with mobile app and then you can control STB via wifi remote using Tata Sky mobile app.
Its all available through easy to navigate GUI (Graphical user interface). So you can use it easily without much difficulty.