So I thought I'd offer some of my experiences with these products.
All of the solutions here are in the end a platform to build products on, some of them require you to ship a "player" version of the platform (Kontakt, Descent etc.) some let you use the platform to build VST/AU type plug-ins (Gorilla, HISE). So here's my take on each of these:
Maise - I downloaded it tried it and yeah its simple to use. But by the time I got round to it I was using Kontakt anyway - and the level of functionality in it was like comparing a bicycle to an Aston Martin. Sure there are times where a bicycle will do, but my experience was that customers in the 2020's want a LOT more than I could wring out of Maise
Descent - same as Maise really - only probably slightly less functionality and UI control. It might work for something with a completely unique sample set - but really not viable for a commercial product in the current market.
Kontakt. I've been building Kontakt products for over 15 years - for myself, partners and customers. It is pretty telling I think at this point that despite 15 years of KSP scripting experience I no longer build anything in Kontakt. The platform is solid, and mature but changes take glacial time to get implemented, NI pretty much ignore feature requests from anyone not in their own Kontakt product team. Despite many comments to the contrary this is the reason large scale developers like Spitfire Audio moved off Kontakt to their own players.
Gorilla. So I was looking for an alternative to Kontakt, and I got involved with this. It was more than 2 years ago, it was a closed and very quiet invite-only thing. So it was early in the development, many things may have changed, but at that time it was missing truck loads of functionality, and was filled with problems - its was pretty counter intuitive to use for a start. As I say it may well have moved miles along the development process by now. But I downloaded it again a year ago and as far as I could see very very little had changed, so I suspect development is going very very slowly. Which was my experience all along - development, and support were pretty patchy. It should in theory be great but it was too much effort and risk for not enough payback for me - so I passed. I never got to the point where I had a testable result. You may have a different experience.
HISE. It took me 2 goes at using this to get to the point where I could build anything useful - but that was 2 years ago, when documentation was scarce. these days it is WAAAY easier. But it's still non-trivial. You will need to understand and install compilers on each of your platforms (Mac, Windows and Linux), additional software like Intel's IPP. I fell over at this point the first time and I've been a software developer for a very very long time. Eventually I took it seriously and got over this "hump" and frankly I've never looked back. It's a lot more powerful than ANY other development platform out there. Virtual instruments and effects are possible, DSP coding, really the potential product range is huge, including stuff like expansions - so yeah you could build a ROMpler like Nexus - in fact I am. I've built about 25-30 products in this now in just over 2 years - a productivity rate I could never have imagined in Kontakt. As I tell potential customers there is (nearly) no reason to use Kontakt over HISE. See that "nearly" there? - Yeah the one thing HISE is missing is time-stretching, so if you want that then Kontakt,or maybe Halion, is your option. However there's stuff here that you dont get anywhere else including authentication/authorisation for your products, server side communications, preset systems, audio encryption(no one can steal your wav files), this list goes on. What me biased?
All of these things have peripheral things that may need doing - like codesigning, notrization and installer builds - but I can talk about those another time if you all like.
So, if you will excuse me, now a quick plug for what I do. Sure you can go through the learning curve for any or a number of these products - but if you really want to be design and recording sounds, and not be code-monkey you *might* think about hiring someone to build your product for you. You do the sounds and the graphics, I do the coding. Give me a call - it costs nothing.
VST/AU Developer for Hire