You get more variance. Full stop. P2pool has higher variance than other pools. The compensation is higher expected earnings from no pool fees, payout of transaction fees, and no risk of being cheated by the pool.
What you say is true, except it really doesn't equate to "higher expected earnings". Yes you can use p2pool with 0 fees, but last I checked, it's frowned upon.
Frowned upon by whom? There is no pool operator to whom you would be paying fees.
Most, if not all pools, now pay transaction fees.
Very few pools pay transaction fees, merged mine for the benefit of the miner, and don't charge a fee. It costs money to run a pool, where do you think that money comes from?
And risk of being cheated by a pool is there, but slim. Most pools are well established, we know who is trust worthy and who isn't.
You don't know with certainty who is untrustworthy until after they have been discovered to be untrustworthy (or incompetent). As you say the risk of being cheated is there, so the "expected" earnings are lower, even if the adverse event hasn't happened yet.
Again, there is no higher expected earnings, unless you purposely choose not to "donate" to forrest.
The higher expected earnings come from the combination of no fees, paying tx fees, merged mining, reduced orphan risk with p2pool, and no risk of cheating by the pool operator.
I stand by my statement, high reject rate increases variance. If that precious share rejects after my 4 day average time to find a share, then, on average, it's going to be another 4 days before I get another chance. And then, there's a 19% chance it'll reject too!
It doesn't really work that way. 80% of the time your share will be accepted! All this means is that instead of a 4 day average time (if that is the number), you have a 5 day average share time.
"normal" pools average around 2% reject rate. That means my chances of getting a reject are 9.5x higher on p2pool than on a conventional pool. How does that not increase variance?
These rejects don't mean the same thing. If the pool average is 19% (I didn't realize it was that high) and your reject rate is 19% then you haven't lost any earnings at all. You are on par with all the other pool members so when it comes time to divide up the blocks you will get your proportional share.