The F-series bars use a triangle-shaped insert so it has 3 usable tips. The one you linked to is a 3/16" right hand carbide shank bar with a 5 degree positive lead that is 4" long. It has a minimum bore size of 0.275 and takes Circle Machine TDAB, TDCG or TDAT inserts. TDAB inserts are flat-topped. They come in various nose radii: TDAB-500 is a 0.002"NR, TDAB-505 is a 0.007"NR, and both come in various grades (CG5, CG6, TN7, CM1, ALO). The TDCG is a ground chipbreaker insert (C = chipbreaker, G = ground) that comes in a 0.007"NR (TDCG-505) and a 0.015"NR and 0.031"NR. The TDAT insert is a pressed-type chip breaker with either a 0.007" or 0.015"NR. Most grades will work fine in a hobby shop. I have most grades and use them all but I really like CM1 for harder steels.
I have not used this specific bar but have used bars of similar type and they work fine. They have zero radial rake but should perform well for you if you need a positive lead bar that takes flat topped inserts. For small bars, the ability to use either a general purpose 0.007"NR insert OR a 0.002"NR insert is really useful. It allows you to do general boring and also do really precisely sized bores. For me, a flat topped insert is a real positive. Not many companies produced flat topped boring inserts.
The key reason I chose the CCBI bars over something like the FCBI that you're looking at is because the CCBI uses inserts with a positive axial rake. This reduces tangential forces and really boosts chip clearance. It is a superior design, in my opinion, but the FCBI bar should be just as accurate. The critical thing we are looking for in a small bar is the ability to take inserts with a really small nose radius and the FCBI bar does that.
I think you'll be fine with it but the price for the bar you linked to is pretty high. I would look for another listing that has a new one of these bars for under $100.00. Be patient and it will show up.
Just so you know, the Circle Machine nomenclature is pretty straightforward. The first letter, like C or F or Q is the series that reflects the insert geometry/shape. C is an 80 degree diamond, F is a triangle, Q is a 60 degree triangle or 80 degree diamond, G is a Trigon triangle insert, etc. The second letter is the bar material - C for carbide, S for steel. The third letter is the function of the bar: B = boring, M = multi-purpose (boring, grooving, threading) and so on. I don't know what the last letter stands for.
If you are interested in Circle Machine bars, search for their catalog that should still be available online. Widia took over Circle Machine and still produce the same bars and inserts. They respond to email inquiries so you can contact them to get the current Widia bar and insert numbers.
By the way, I happen to agree with your choice of HSS cobalt bars for the mill. I think you'll find them very useful.
