I was reading through Nevatech Sentinet the last week and I'm currently asking myself the following question: "When NevaTech Sentinet exists, with all these named features, why should anyone use BizTalk with ESB Toolkit and extend it with Sentinet?"
Does I see there something wrong, but Sentinet is able to handle everything and more what BizTalk with ESB Toolkit is also able to do?
Essentially you are talking about 2 very different products here.
Sentinet is a very good tool if you are thinking about centralized API management. It is very good in what it does in that niche.
BizTalk on the other hand is a ESB, using a publish/subscribe architecture. BizTalk also has various ways of connecting to non-trivial systems like SAP, DB2, Siebel, MSMQ, etc... It can also do EDI/AS2/X12, flat file parsing and so on. You can set it up as a ESB and/or message broker/hub/etc...
In your specific case (I'm guessing web services related?) it might seem that BizTalk and Sentinet are similar, yet the two are very different and actuallly complement each other rather nicely.
As you see these are 2 completely diverse products and together they actually might be a perfect match in your case.
Some more clarification after your comment:
Using BizTalk does not necessarily mean you have to use ESB Toolkit. BizTalk can perfectly act as an ESB without the ESB Toolkit.
The benefits of using Sentinet is definitely API management. What you are focusing on when "doing" API management with Sentinet is to form a single layer of API's within Sentinet. Often you would point all your clients (both internal or external) to Sentinet, where you would host all of your services virtually. You gain a lot of control that way and can add security, versioning, load balancing, SLA reporting, etc... to your existing services without any hassle. Another thing Sentinet is quite good at is low-latency services. This is something BizTalk is not particulary good at, since it will persist everything to it's database to prevent losing messages. (I once used it in a POC and setup a virtual service calling an existing, external service with additional enrichment and easily covered 200+ trx/seconds).
BizTalk on the other hand is middleware. That's a whole other playing field.
It's very good in connecting different systems to each other using different protocols, mapping messages to other formats (xml, flat file or EDI), adding business logic to your flows, integration patters, long running flows, loose coupling, etc... you wouldn't want to use it as a virtual service since it will persist everything to it's message box!
Hopefully now you see they are both quite a different tool set.
They do play along nicely next to each other though: hosting your BizTalk web services in a virtual web service on Sentinet has a lot of advantages, especially in a fast-paced environment.