What is the difference between Zero mobile and Zero1? Both don't seem too good?

Both is good

So let’s weigh the plans of zero and zero1 assuming we are a high internet user/talktime.
As for Zero,

Plan 1 : you can get unlimited data,calls and sms at $69.95/month, which will give you unlimited data at 4G speed, but in accordance to fair use policy. There’s an ongoing promotion now for $59.95/month. There is no binding contract.

Plan 2: If you are a high internet user, you could also take unlimited data at $49.95. Right now promotion at $39.95 which is a good deal.

As for Zero1,

Plan 3: You pay $39.90 for 9GB to unlimited data Where first 27GB would be at 4G speeds.free talk time of 450 mins ( incoming and outgoing each)

Plan 4: You pay $29.90 for 3GB to unlimited data Where first 15GB would be at 4G speeds. Free talk time of 200 mins ( incoming and outgoing each)
This means that its better to use ZERO1 (PLAN 3/4) if you would like a cheaper alternative best is to pay $29.90-$39.90 where your data of max 15-27GB would have high speed, with additional free talk time as a bonus as compared to only unlimited data through ZERO.

Otherwise, if you have not much of money constraint and also someone who would spends lots of time talking on the phone, best is to take Zero plan of $69.90 which is now going at $59.90 . Where you can get unlimited calls/data/sms, which means you no need to worry on how much you use your phone since the monthly payment should be constant thoughtout which is so convenient .
Zero1 offers “unlimited” data too at less than half the price ($29.99/month), but you only get 3GB of data at guaranteed 4G speed – any data beyond that is at “managed speeds”, whatever that means.