Startup w/ buddy?

Know someone for a long time and they have quit their job to start a startup, and basically want me to take over tech side. Should I join? 1. Corporate job pays really well compared to hours I put in. Manager and team are all reasonable people. It's CRUD and not satisfying. 2. I tried to work on product in free time, though the startup work is all CRUD and doesn't really engage me after work hours. Would require serious discipline to do this. 3. Friend is occupied himself with investors, slide decks, cap tables in different series of the company, recruiting, .. to me it seems this is cart before horse, and lack of spending time on the product esp. given they have good technical ability is a red flag. 4. Equity offer is good, 5-10%. 5. Friend sometimes takes business stuff really emotionally/personally and I am detached from work, even when I work hard it's just work and I'm not gonna get angry or personal about it. 6. Friend has history of abandoned business ventures.