It is alot better than you think, I fact it is vastly superior to the o5e artificer.
- 1st level O5e 2 1st level spells / A5e 2 1st level, roll a d4 on a 1 they run out of charges. So you have a 75% chance to cast more spells.
- 5th lvl o5e 4 1st level spells, 2 2nd / a5e 6 devices can be up to 2nd level, 2 roll a d4, 2 roll a d6. Drastically better than o5e. So same number of spells, but a 75-83% to recast 1st level spells, and a 50-66% chance to recast 2nd level spells.
- 9th level o5e 4 1st, 3 2nd, 2 3rd / a5e 9 devices that can cast up to 3rd level 3rd level spells have a 25-50% chance of being able to recast.
This just keeps getting better because at 10th level the fizzle dice increases making it easier to cast low level spells over and over, at 11th level you reroll 1s. By 13th level you have 1 more device than an o5e artificer has spells and keep that all the way through 20th level and at 20th level your fizzle dice grows again.
So the a5e can cast 1 more spell per day guaranteed, can up cast all of their spells to their heights spell slot I they want and have a good chance to cast the spell over and over again and can practically cast 1st level spells as often as they would like.
The engineer and the sticher get hit hard with the fact that they will be sacrificing their spell devices to power their modification which I am not sure is worth it.