Trying with big amounts is even more dangerous, especially when arbitrage opportunities usually arise from exchanges such as HitBTC, Yobit, etc. that hold ambiguous regulatory statuses and a history of less than reputable behaviour. You may be putting your capital at risk here even if on paper this trade is guaranteed profit.

And that is basically the flaw of all of these calculators - they don't take into account the fact that most of the times when these arb opportunities arise, it's because of inefficiencies (disabled/delayed withdrawals, for instance) that make prices inaccurate. It doesn't necessarily mean you can take advantage of it without risk.

Add a pricey monthly subscription... I'm not sure about that at all. At least sites like BitEdge push notifs for arbs for no cost.