After owning & using a SIG and several of the Umarex models, in ALL areas I'd recommend the latter. Walther CP88; CP99; Beretta 92FS; RWS C225; Colt 1911 (with target sights) and probably the most accurate one, the S&W 686, although none of those feature blow-back action. I have a Umarex Desert Eagle for that! Still got them all! Did own a Umarex Hammerli 226 and that was certainly OK and definitely of better construction than SIG's own version. I'd always go for a pistol with at the very least, lateral adjustment of the rear sight. My S&W 686 & Colt 1911 adjusts for height as well. I use GECO flat-heads in all my Umarex pistols. Accurate & inexpensive at around £4-£5 per tin of 500 depending on how many/where you buy from.

Plenty of good pistols to choose from out there!