Download prior version of Specflow .vsix - visual-studio-2017

Question

Our team supports the automation efforts of users who are on the latest version of Specflow, as well as those who are not. So the need exists to bounce between the current .vsix for Specflow on VS2017, as well as the .vsix that expects Specflow 2.1 (right now I'm stuck because any feature.cs regeneration fails with a can't find 2.2). I did attempt pulling from https://github.com/techtalk/SpecFlow.VisualStudio/tree/release/v2017.1, but am getting several unresolved references to Microsoft.VisualStudio.
Any way to simply pull the .vsix that works with SpecFlow 2.1?
Edit: Thanks Andreas, the fast response is much appreciated. I will go ahead and open an issue on GitHub if you wish, but I didn't mean to imply that there is an issue with the extension. It may well be a misunderstanding on my part - I though that the current Specflow VS Extension 'expects' SpecFlow 2.2.
As you know, SpecFlow 2.2 uses NUnit 3.x, whereas SpecFlow 2.1 uses NUnit 2.x, which is essentially a breaking change for solutions that used obsoleted features of NUnit 2.x.
So when I switch from a branch that used SpecFlow 2.2 to another branch that uses 2.1 (even tried clearing AppData/Local/Temp), the SpecFlowGenerator will fail because it's looking for SpecFlow 2.2, which we don't want to use in the pre-conversion branch because of the NUnit issue.
I'd love to not have to swap out the extension, as long as I can continue to switch branches between one that uses SpecFlow 2.1 and one that uses 2.2. The app.config for the project does contain a binding redirect -
<dependentAssembly>
<assemblyIdentity name="TechTalk.SpecFlow" publicKeyToken="0778194805d6db41" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-2.2.1.0" newVersion="2.1.0.0" />
</dependentAssembly>
So the question is how to use the up-to-date extension even when bouncing between branches that use 2.1 and 2.2. Thanks again!

Answer 1

The Visual Studio extension supports all versions of SpecFlow from 1.9 up to 2.2.
If you have problems with it, please open an issue on GitHub, so that we can find the reason together.
Update:
SpecFlow has no direct reference to NUnit. Not with 2.2 or anything before. There is a NuGet package SpecFlow.NUnit which has a package dependency to NUnit, but this package helps only configuring SpecFlow for NUnit. But you don't need this, when you are doing the configuration manually (setting the unit test provider to NUnit in the app.config).
It could be, that when you are switching branches and don't restart Visual Studio between, that we have still a reference to the previous SpecFlow assemblies and so a Version hickup is created.
Full disclosure: I am one of the maintainer of SpecFlow.

Answer 2

In case anyone else wrestles with this, here's the fix that worked for me with this particular sequence of events
1) you have a branch that uses SpecFlow 2.1
2) you upgrade to the latest VS SpecFlowExtension
3) you switch to another branch that uses SpecFlow 2.2 and successfully have the feature.cs generated
4) you get a request from a user needing support on 2.1, switch to that branch, make a change to a feature file, and get slammed with SpecFlow 2.2 not found
5) even after closing all instances of VS, deleting LocalAppData/Temp/VisualStudioTestExplorerExtensions, starting VS and opening the solution that uses the SpecFlow 2.1 drivers, then attempting to save still results in SpecFlow 2.2 not found, even with a binding redirect to 2.1
Apparently something is cached to disk (reboots didn't help) that isn't immediately apparent. The solution was to have separate clones - one for the branch that referenced SpecFlow 2.1 and an entirely separate clone for the branch that referenced SpecFlow 2.2.
Now I no longer get SpecFlow Generator errors - the trick is not to use separate branches, but separate clones.