Again, I dont think there are many apps that use it.
You're limiting yourself when you do use it because all your users will need to be admin on their machines.
For that reason, most companies have made their own device drivers or have borrowed someone elses.

However, being in this for fun and not money, SPTI is great for me. Most people buying machines will get them with XP installed. For them, DVD Decrypter will just work straight off because they'll be admin already. That puts me 1 step ahead of SmartRipper that still requires ASPI for device authentication.

Using SPTI isn't really any harder than using ElbyCDIO - from a programming point of view anyway! It's a bit fussy about having 'aligned' buffers for large transfers but that's about it.

What really gets on my nerves is when people think changing the Interface type from SPTI to ASPI or whatever will cure their 'No Seek Complete' error! In my experience (speaking about DVD Decrypter of course), if SPTI works at all, stick with it - it will be fine. Its not a half and half thing and I dont think there are any speed advantages to using any one interface type over another.
Being a built-in 'Microsoft' thing, I would have actually expected SPTI to be just about as 'Low Level' as it gets.
Of course Olli might have a different opinion having written an alternative!
Big thanks go to him for that - and for allowing DVD Decrypter to be the only 'Non Elby' tool to support ElbyCDIO!

So in short, SPTI is great because its one less driver you need to install. It's just a shame Microsoft didnt make it so 'normal' users could take advantage of it too.