Is the S2 enough?
For a first bidet, usually yes. The wash itself — which is the point — works the same way as on the more expensive models.
Most people who upgrade later do so for the dryer or for unlimited warm water, not because the cleaning was lacking.
What the S2 includes
Front and rear wash with adjustable pressure and position, a heated seat, warm water, oscillating spray and a self-cleaning wand.
What it does not have
No warm air dryer, and no auto open-close lid. Water is heated in a tank rather than on demand, so it lasts around 40 seconds before reheating.
If a dryer matters to you, the S5 is the next step up.