I have done several. yes, you can pick them up from the bottom and that makes them maintainable from the surface, but you really need trip lines for that. the trip lines will make a close circle with you proposed distances.
i have found it is far easier, and just as good with large anchors, heavy chain and two, instead of three points. much easier to lay, easier to get up, etc. i don't think the join point get far off the bottom under normal use.
37' sailboat. I used 1/2 inch chain, 60lb plow anchors, and trip lines. set it at low low tide, or you can pull on the trip lines (away from the other anchor) to get the widest set. with a wider set, the scope the anchor sees is very large. this is in soft mud. i have had no issues of anchor movement, even in 70mph winds and 3' close set waves. this is the worst this anchorage gets in the winter.
i think a concrete block is cheaper if you can do it yourself. helix must be large and deep for soft mud.