Here's the basic canned response you'll get regarding interactivity with the Slingbox and unreleased products.
Dear <insert your name here>,
Thanks for participating in the Slingbox Answers Forum! We don't comment on unreleased products or release dates here, but we can tell you that we are working hard on update to SlingPlayer Mobile for <insert brand here> that will be a great user experience. Here's a link to a great FAQ page on our website with answers to the most common questions about the Slingbox:
Here's the basic comparison between the two
Watch and control multiple devices - including your standard- or high-definition DVR, digital cable, satellite receiver, or DVD player - from anywhere on your computer or mobile phone.
Now regarding mobile streaming to the HTC EVO 4G. Since it comes with 800 x 480 pixel resolution, it is not considered a high definition display. The nice thing about both Slingbox models is that it will adjust its transcoding output resolution based on the client that is connected to it. So, not only does it provide a good quality picture but it also ensures a minimal bandwidth requirement. Which is 150 Kbps or higher for the Slingplayer Mobile.