To answer the last question first the SC-150 would be the Seacam 150 which comes in two types I believe.
Regarding the Inon Z330 type II you can read my full review in the current issue of UWPMAG.com which is a free PDF download. I have also used the Ikelite strobes extensively and if you go to the back issues at the top of the home page and enter Phil Rudin into the search engine you will find my DS-161 review along with other Ikelite equipment I used with the strobes.
I owned the first two Inon Z-220's imported into the US and have owned or tested about every Inon strobe since. Since I do a good bit of travel (before covid) I can attest to the fact that they are about as easy to travel with as just about any strobe on the market and take up about half the space of the DS-161's. I tend to use two strobes for both Wide and macro shooting and find the Inon's more than enough coverage all the way out to 8mm circular fisheye and full frame fisheye. The down side to most strobes are hot spots that blowout light areas in the frame. This is noticeable when shooting things like the light face of the loggerhead turtle closeup. The new "fly-eye" coating on the dome of the Inon type II strobes helps greatly in this regard. I also own the inexpensive (around $11.00 US) dome filters that allow you to change the color temp of the light to 4600K and 4900K.
I have not yet tested the Retra Pro-X strobes but I hear good things about quality of light and more. High quality light is a small addition if you are not using high quality lenses and ports.
Most photographers when they are shopping for strobes or other equipment usually have a price point in mind and many not consider comparing a $650.00 US Inon Z-330 type II to a strobe like the over $1300.00 US Retra or even the $950.00 US Ikelite DS-161.
Other considerations may include proprietary batteries that won't easily be found in many travel destinations. Ikelite has great TTL performance when used with wired cords and an Ikelite housing. They don't integrate as easily over to other housings if TTL is required. Converting Ikelite to fiber optic cords also adds cost to the strobes not found in the Inon, Retra and others.
Images of the Z-330 and Z-330 type II attached along with the turtle taken with the type II. You can see that the Z-330 has the "fly-eye" but only on a small stand over the flash tube.


