Mixed, I think. Some feel clean tank and petcock screen intact should be sufficient. I feel if they are installed correctly, lines aren't cramped to kinked trying to do it, and you don't have flow issues, why not? I use them.
Well, Bob, then I have have to ask. How do you know that two filters are enough? Surely, if you put five or six filters in series that would be even better, right? Can't get that fuel too clean, now, eh?
Just joking.
Filters are selected by their particle size rating and block particles larger than that rating. As they trap particles they become more restrictive and block ever smaller particles. This usually reduces their flow rate while they are used, depending on the concentration of the contaminate supply.
If the goal is to keep fuel orifices in the carburetor flowing, you need to block particle sizes that won't fit through those orifices. Other, smaller, particles flow though and that helps to maintain a cleaner overall system. Trapping unnecessary particles adds extra maintenance chores, such as periodic cleaning, replacement, or flow testing. Add installation issues to the experience, and I don't see why extra fuel filters are recommended by so many.
For those championing the added filter philosophy, do you even know what particle size is being blocked by your added filter?
Or, is this addition more to make the owner feel good, rather than actually improve operation of the machine?
Or, do you just think others should make the same expenditures you have, so you don't feel as foolish? No insult indended, there is real human psychology behind these questions. Not all we do is rational or logical.
Certainly filter your fuel. Spend as much effort, time, and money as you feel appropriate to the task.
Cheers,