When you open a crypto DEX, you are really choosing between two kinds of market: a liquidity pool and an order book. A pool is fast and always available. An order book fills only when a real counterparty is on the other side. If a DEX burned you before, the pool was almost certainly what did it.
A Crypto Dex can route your trade either way, but the pricing logic is not the same. A pool prices from a constant-product formula, x·y=k, so as you buy, the ratio shifts and the next token costs more. An order book prices from actual bids and asks, so your trade either crosses to a resting order or waits for one. That is the line: a formula sets your price on one side; a real order sets it on the other.
The default swap button is usually the pool, because the pool can always take your order. That convenience is the catch. With a pool, your execution is a public transaction that reprices the pool, which is exactly what a sandwich attack needs. The order-book side is the safe path, and the move is simple: place a limit order, not a market swap.
Say you want to buy ETH at 2,500. Enter that price; your order sits on the book. If a seller crosses, you pay 2,500 plus the exchange fee. If nobody crosses, your money stays with you. You do not pay price impact, and no one can push a pool balance against you, because there is no pool. The fill price comes from the spread in front of you, not from a formula repricing your own trade.
The one condition is depth. If the best ask is 2,501 and only 0.1 ETH is resting there, a 5 ETH order will eat through several price levels. On an order-book DEX, you can read those levels before you commit. If the depth is not there, do not trade. That is the whole safety: you are not trusting a protocol's promise. You are reading the commitments of actual counterparties, and you walk away when those commitments are not enough.