how well do usb 2.0 to vga adaptors work?

[Ashley MLP Fangirl]

ok, so here's my situation. i need to do a presentation in a few weeks, which i made in Keynote (apple's version of powerpoint basically). the problem is, the display output on my Mac is dead. so i can't drive any external displays using the gpu in my Mac. 

 

now, i found some usb 2.0 and usb 3.0 to vga adaptors, which i assume have their own gpu in them. however, my Mac doesn't have usb 3.0. i found a usb 2.0 one that had a max resolution of 800x600, which is really awful... 

i need to ideally have 1080p, because i have a lot of visual effects and stuff in my presentation. i don't care if it's at 30 or even 24hz, but i need full resolution... 

 

so how well do those usb adaptors work and will they work with a system that has a broken gpu? 

(the story behind that is the amd gpu in my model of MacBook often fails, google radeongate, so i disabled it so that if it breaks i can still use it, be it on intel graphics. the display output is wired to that amd gpu, so that doesn't work anymore)