I'm glad your situation turned out positive for you.

However the reason why the foreign teacher should never accept an offer to enter on an L visa is for the teacher's own protection. Two points:

1) It shows the school can legally hire foreign experts, not just promises to get a Z or F visa after arrival.
2) If the teacher is working illegally in China on a L visa(even temporarily), they won't receive any help from the PSB or FAO if needed, despite any promises to them by the school or any contract they may have signed and while working on the tourist visa.

The teacher has everything to lose and nothing to gain by starting to work as a tourist. The school gets a foreigner they can 'test drive' for 1-3 months, and if anything goes sour can fire the teacher on a moments notice, force them to leave their apartment and have most or all of their pay withheld. What can a foreigner do in if this situation happens? Nothing.

When foreigners enter China on a Z visa, they have the knowledge the school's paperwork is 100% legit(rather than finding out after the fact it isn't) and the assurance that if they do have any issues with the school, the PSB / FAO will be there to assist.

Start your teaching career in China on the right foot by choosing a quality, legit school that is willing to give you the paperwork for the Z visa BEFORE you enter China, not after.

I reiterate my point that you should NEVER enter on a tourist visa. Despite whatever the school may tell you, it is not okay! Its illegal and if anything goes wrong...you're gonna have a bad time.