what are difference between those three model
You Can check their official website.
Out right model- HD 3,500rs, SD-3k
This model allows customer to avail a new DTH connection - Set Top Box and accessories, (full over price)
Rental model- HD-3,500rs & SD-3k
This model allows customer to avail a new DTH connection - Set Top Box and accessories on monthly rental basis.Customer is required to pay a security deposit which is refundable.
Enstrument model-HD-932rs SD-898
Most popular and preferred model which provides best in class DTH.In this model Sun Direct owns all the rights on equipment and accessories.