From an electricans viewpoint,
Sundance is my choice since I've wired 200 or more over the years.
I believe that they outperform all the rest..and I've seen many different brands!
New at this posting forum so bear with me.
Your tub will indeed work on 50A mode although #6 THHN Copper shoud've been used for your line conductors, #8 greenfor your equipment ground.
Always check your spa owners manual for this info first.
Don't know much about Sundance tub color matching..but I would suggest you utilize the 60A GFCI option on this model.That way you'll be able to use all the bells and whistles simultaneously.
Square D QO260GFI is the special neutral absent breaker you need for this install.