If you're deciding over a €120 price difference, going with the Latitude 5450 is definitely the smarter choice. I actually found a Dell Latitude 5450 deal (CO-Computers e.K.), and I've had really good experiences buying from this seller in the past.
The 3450 is Dell's budget entry-level model. It gets the job done, but the all-plastic body feels a bit cheap, and the screen is fairly average and dim. If the laptop is just going to sit on one desk and never move, it does the trick, but it isn't particularly exciting or premium to work on.
The 5450, on the other hand, is a noticeable step up. It's built with higher-quality materials, making it feel far sturdier and more durable. The screen is brighter and much easier on the eyes during long work sessions, the keyboard typing experience is better, and the webcam is clearer. Connecting it to external displays and desktop setups is also much smoother and less finicky.
Since this is a laptop you will likely use for years, that €120 extra pays for itself very quickly in comfort, better build quality, and a much nicer overall experience. Go for the 5450.
Best regards,
Markus