Well I used a Tria so I’ll give you my honest experience:
It doesn’t give immediate results. Each time you use it, it takes three weeks from the date you use the device until the hair actually sheds (similar to how long a pro laser takes). In the meantime, the charred hair is difficult to shave over so you have to commit to three weeks of stiff, pokey hairs that look like a five o’clock shadow.
But if that’s okay, then you should get a few weeks of (near) hairlessness. I shed maybe two and a half weeks ago on my arms and most of the hair hasn’t grown in yet. Just some wispy bits that I suspect were missed altogether. Hair in certain areas grows at different rates, but I would guess you’d be clear for more than 2 weeks, but less than if you had waxed normally. Prolly longer than that on your legs because I heard leg hair grows fairly slowly.
That being said, it’s nearly impossible to get a good overlap with the Tria (dunno about the Silk’n) so you probably won’t get 100% shedding. I thought I did a thorough job but only 50% and 70% shed on each arm.
Your hair may or may not grow back finer (if you use it lots, it will probably get more fine and limp to the touch, so that might help with ingrowns in the future).
Overall, I used the machine once and realized that the time involved (and $80 replacement bulbs for the Silk’n) actually make it more expensive than pro laser treatments. For $100 every 3 months (a tiny expense, even at 6-8 sessions), you could be done FOREVER with 95% of the hair in the area of your choice. For me it was a no brainer, and I asked my family for pro treatments as an early Christmas present.
If you truly don’t have the money to spend on pro laser, I’d vote you spend a year saving until you DO have the money. But the companies are reliable so I see no reason why you can’t give it a try and just return it if it’s too high maintenance.
P.S., being stubbly one day after shaving doesn’t sound bad at all! I’m jealous! I get stubbly within two hours of shaving, no matter how perfect of a job I do.