Hello Zoonnoasi30
Yes, what concerns trains, buses, trams, and boats, the Saver Day Pass offers the same validity. However, not so for the mountain excursions where the Swiss Travel Pass (not SwissPass) may offer dicsounts while the Saver Day Pass does not (and is not valid at all).
Yes, the Saver Day Pass covers the journey from Bern to Grindelwald. See the validity map here (section Downloads):
https://www.sbb.ch/en/tickets-offers/tickets/day-passes/saver-day-pass.html
The Saver Day Pass is not valid to First or Kleine Scheidegg, for example.
Is the Saver Day Pass the best ticket in any case? It depends. Given the fact that its price is raising the higher the demand and the nearer the day of travel, a regular point-to-point ticket could do as well. Compare tickez costs for each journey on www.sbb.ch
And, the Swiss Half Fare card offers additional discounts:
https://www.sbb.ch/en/tickets-offers/tickets/guests-abroad/swiss-halffare-card.html
For children, the Junior card (paper ticket from the counter) is a great bargain. Alternatively, the Day Pass Children.
Let us know if you have got more questions.
Kind regards,
Roland