When I started out the tank I had 10 but these dropped off one by one over several months. This is another thing to consider as the rainbows are relatively expensive (since lockdown I think LFS has bumped the price up to something like £15 for two

) but I have seen some better looking stock at a shop about an hour away which are three for £9 but are pretty small. Tempted to order some from Sweet Knowle Aquatics if I do get some( (which look to be £24.75 for six)
I have been looking at the bloodfins as they seem pretty suited to my hard water and look like they school / shoal more than others. (Even when I had a lot more black neons they never really shown any interest in each other). They also seem pretty active fish to add some movement to the tank.
The bloodfins look quite nice when you see pictures like this

But I suspect this isn't typical and is more likely the lighting or Photoshop editing. Other photos seem a bit more silver with red fin tips and others look just silver with very little red (which is how they look in the shop)