I would never tell you NOT to purchase anything from Inventables. However, if you have a Triquetra Touch Plate it can be used in place of the Inventables zero touch plate but will only work as a Z Zero touch plate if used within Easel. To get the full benefit of the Triquetra you will have to use it with another software package such as Universal G-Code Sender or Pic Sender. There are others that are supported. Once you have zeroed your bit with the Triquetra and something other than Easel, you can return to Easel and still have the benefit of having zeroed your bit to all three axis and use Easel to design and carve your projects.
As for homing switches, well you will receive a mixed lot of answers on that subject. I myself never use them. I tried and spent way too much time trying to get them to work properly. If you zero all three axis with a touch plate then you really don't have a need for them. It is possible to use them as limit switches which can be beneficial if you accidently try to exceed the travel limits but again, I never use them at all. There are fixes for the issues I have experienced with the switches but I had more important things to do that try to chase RF noise interference problems with something I don't feel that I needed.
Hope this helps you make your decisions,