Optional Two-weapon Fighting Rules

Since the World of Onn clarified the way I use Two-weapon Fighting (TWF) in my games, I've been giving it some more thought. Now, there are always dissenting opinions (and I welcome them here or through emails) on what guidelines or processes work 'best' or how to better reflect historical accuracy or make it more player friendly (ie, removing any TWF penalties). A long ways back I had thought of an alternative to the TWF Penalties Chart:

When TWF with an allowed off-hand weapon, the character's attack with his off-hand functions at half the character's actual level. If the character is using a weapon in his off-hand not on the allowed list, his offhand attacks at one-quarter of the character's actual level. Lastly, if the character is not proficient in TWF, his off-hand attacks are always made as if he were 0-level. Off-hand attacks may never make more than one strike per round.

This chart should help make things more clear for any math challenged among us (I know I am at times, and besides, I like charts!):

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Two-Weapon Fighting Attack Bonuses

Character Level	Primary Weapon	Off-hand Allowed Weapon	Off-hand Not Allowed Weapon	Unskilled Off-hand
1-2	+1	+0	+0	+0
3-4	+2	+1	+1	+0
5-6	+3	+2	+1	+0
7-8	+4	+2	+1	+0
9-10	+5	+3	+2	+0
11-12	+6	+3	+2	+0
13-14	+7	+4	+2	+0
15-16	+8	+4	+2	+0
17-18	+9	+5	+3	+0
19+	+10	+5	+3	+0