NavList:

I'm just throwing a few observations in here - worth every pfennig you pay for it.  :-)

I have the Frieberger 4x and find it just fine - I like the Tamaya 4x a little better but these are fairly simple telescopes to begin with.  I personally find the 4x scopes sufficient compared to higher magnification scopes as the wider field of view on the 4x scopes helps me find stars quicker.  If you are doing lunars, then perhaps the higher magnification will help with accuracy.

I have a preference for the full horizon mirrors.  I didn't learn that way but I just like them better.  There is less reflection from them so some dimmer stars may be harder to find in a full horizon mirror.  That said, either method works fine - I find a little bit of side error in the mirror can be a good thing for traditional mirrors.

I live in a forest far from anything that might be called a horizon (pond?) and most often use aviation octants with a bubble.  With a bubble octant, if you can see it, you can shoot it.  (I can do that, too, with a nautical sextant using lasers - see: NavList: Re: Ex RNZAF navigator keen to learn marine sextant ways (151660) (fer3.com))  I doubt you'd want to try and use a bubble octant on a small boat - the bubble is a lively thing.

There are many aviation octants out there - I am partial to Kollsman periscopic octants.  the A5851 is another one that I have and it is a solid instrument.  The Link A12 is also an excellent instrument and considerably simpler to use.